The World Baseball Classic is part international baseball tournament and part ominous cloud of mystery for Major League Baseball players.

There are two chief fears regarding the WBC. One is that playing in it will result in an injury. The other is that stepping away from a regular spring training routine will lead to complications during the regular season even if a player does keep his health during the tournament.

ESPN's Jayson Stark would have everyone believe that the injury concern factor is overblown. He presented some numbers in January that prove there's little real injury risk associated with the tournament. In fact, the last two WBC years (2006 and 2009) saw less than nine percent of MLB's players begin the season on the disabled list.

So as far as the numbers are concerned, the WBC is not an injury bug intent on getting all of MLB's best players. The players shall rejoice to hear it (if they're in a rejoicing mood, that is).

But even if you take that away, the WBC still has an ominous cloud of mystery thing going for it. It may not lead to injuries, but does it impact performance? 

Taking separate looks at hitters, starting pitchers and relief pitchers, here's what I found out.

Hitters

Hitters have it easier than pitchers when it comes to the WBC. Whereas pitchers have to be careful with their arms, hitters just have to grip it and rip it and do their best to stay out of harm's way.

By this logic, their participation in the WBC shouldn't hurt their production.

Well, let's see. For both the 2006 WBC and the 2009 WBC, I gathered collections of hitters who saw a significant amount of action in the tournament and who also played in at least 100 games in both the previous season and the ensuing season. This was for the sake of avoiding too much injury-skewed data.

Under normal circumstances, I'd use wOBA as an offensive measuring stick. But since no wOBS are kept for the WBC, OPS will have to do for an offensive measuring stick.

So there are the ground rules, and here is the first table for the 2006 WBC.

The final count: 17 players, nine up trenders and four even and four down trenders. In and of itself, that's an encouraging sign for hitters thinking of participating in the WBC one day.

A closer look says they should wait just a second and think about what really went on here.

Of the four even trenders, the only one who hit particularly well in the 2006 WBC was Ichiro. It helped that he had his walking shoes on, drawing four walks in eight tournament games. For him, that was an unusual amount of patience in a short amount of time.

But in no time at all, Ichiro was back to his usual self in 2006. About the only thing that changed from his 2005 season was his power, as he hit only nine home runs a year after hitting 15. The trade-off was an elevated BABIP that led to a higher batting average (see FanGraphs), which was bound to happen.

So the WBC didn't seem to help Ichiro all that much, and it didn't seem to hurt Miguel Tejada, Willy Taveras or Bobby Abreu. All three had their issues in the WBC, but all three shrugged them off and kept on hitting at their usual pace in 2006.

As for the four down trenders, two of them declined after strong showings in the Classic: Jorge Cantu and Ken Griffey Jr.

Cantu had a good excuse for his .699 OPS in 2006. He had a problem with his left foot right out of the gate and eventually had to go on the disabled list with a fracture in late April. He had a solid .814 OPS at the time he went on the DL, but he managed just a .681 OPS the rest of the way. 

Stephen Dunn/Getty Images

Griffey hit three homers in the 2006 WBC, but didn't improve on his 2005 season.

Griffey also had his typical problems with injuries in 2006, but he still hit 27 homers a year after hitting 35. The big difference in his performance was a BABIP decline that he was due for after his BABIP spiked in 2005 (FanGraphs). Basically, he came back down to earth in 2006.

Alex Rodriguez and Juan Encarnacion also came back down to earth in 2006, though not disastrously so. Asking A-Rod to repeat his 1.031 OPS from 2005 was asking a lot, and Encarnacion's .795 OPS in 2005 still stands as a career-best for a full season and well above his career norm of .758.

As for the up trenders, a couple of them had nowhere to go but up after down seasons in 2005. This group includes Bernie Williams, Carlos Beltran, Adrian Beltre and Omar Vizquel. All four of them had strong seasons in 2006 after showing well in the WBC, which suggests that the Classic can help a hitter find his wits.

Then you have the notables who improved on already solid production after the WBC: Albert Pujols, Derek Jeter, David Ortiz and Miguel Cabrera. Their 2006 performances are not easily chalked up to the WBC, though, as Pujols and Ortiz were in the prime of their power-hitting years, Jeter was still only in his early 30s and Cabrera was fresh off his first .900-OPS/30-homer season.

This leaves Ivan Rodriguez as the biggest wild card of the up trenders. He had his worst season in many years in 2005, didn't do much better in the WBC and then proceeded to raise his OPS by 34 points. It's possible that was due to him getting some reps in at the WBC.

So of this bunch, none of the four down trenders can have their poor performances chalked up to the WBC, and a couple up trenders who can have their strong performances chalked up to the WBC. For everyone else, it was business as usual.

Now on to hitters from the 2009 WBC.

The count: 18 players, seven up, seven down and four even.

Two of the even trenders—Cantu and Jose Lopez—mashed at the Classic. Both hit two homers, and Lopez hit six doubles to Cantu's five. They thus both benefited from huge slugging boosts.

Lopez sustained his in 2009. He upped his home run total from 17 to 25 and his ISO (Isolated Power) from .146 to .191 (FanGraphs). His power surge looks like a fluke in retrospect, but it may have been a result of him swinging for the fences after his big showing in the WBC.

The two other even trenders—Abreu and Kevin Youkilis—did their thing following the WBC. They both hit well in the event, but you'd never tell just from looking at their 2006 performances.

Jim McIsaac/Getty Images

It's unfair to blame Wright's power decline in 2009 on the WBC.

Among the down trenders, David Wright's big drop-off in performance following a subpar showing in the WBC looks like a red flag. However, two things helped drag his numbers down in 2009: health issues later in the year and Citi Field. Using either ISO or slugging as a measuring stick, he hit for less power at home than he did on the road (FanGraphs).

Down trenders who were due for a decline in performance one way or another in 2009 were Melvin Mora and Mark DeRosa, who both overachieved in 2008 with clear outlier OPS's. DeRosa's power spiked both in 2008 and in the WBC, but his slugging percentage and ISO both dropped in 2009 despite a career-high 23 homers (FanGraphs).

Elsewhere in the realm of down trenders, Alex Rios' OPS showings had been in decline ever since 2006, and Jimmy Rollins saw his OPS take a huge tumble in 2008 following his MVP season in 2007. The two of them were in deep water before the WBC, and neither was able to use his strong performance in the tournament to rebound in 2009.

Similarly, Ordonez's power declined greatly in 2008 following his near-MVP season in 2007, and he gave little indication in the Classic that he was going to rescue it. Sure enough, he didn't.

Pudge Rodriguez is another story. He went into the 2009 Classic after having posted .714 OPS's in both 2007 and 2008, and it looked like he had a shot to do at least that well in 2009 following his explosion in the WBC. He did end up increasing his homers in 2009, but he didn't dramatically increase either his ISO or slugging percentage (FanGraphs). It was a tease.

Among the up trenders, Ichiro, Cabrera and Jeter all rebounded in 2009 after down years. The fact that none of them greatly improved on their 2008 performances in the WBC suggests that the tournament didn't make much of a difference for them. The same can be said of Kosuke Fukudome, who improved on a strong rookie season in 2009 despite a poor showing in the WBC.

Adam Dunn is not in that same boat, but his spike in production following his outburst in the WBC is misleading. He did up his OPS in 2009, but it wasn't because of a huge spike in power. It was largely due to an uncharacteristic BABIP spike (FanGraphs). Ryan Braun enjoyed a similar benefit, as his production turned around in 2009 thanks to a BABIP correction (FanGraphs).

Kevork Djansezian/Getty Images

Gonzalez hit two homers and slugged .636 in the 2009 WBC.

This leaves Adrian Gonzalez as the wild card among the up trenders. Gonzalez showed off some power in the WBC and then went on to hit for more power than ever before in 2009 with 40 homers and a .274 ISO (FanGraphs). He also walked 17.5 percent of the time he went to the plate. All of this is evidence of a man in a zone, and Gonzalez clearly first arrived in said zone during the WBC.

So among this group, Lopez and Gonzalez stand out as hitters who got in a groove in the 2009 WBC and stayed in said grooves in the regular season. Everyone else pretty much carried on as they'd been carrying on.

All in all, there are 35 different cases recounted above. The breakdown is: 16 up trenders, 11 down trenders and eight even trenders. Based on that data and the fact that many of the downers can be chalked up to forces other than the WBC, the Classic is more likely to either help hitters or make no difference at all than it is to hurt them.

Hitters, therefore, shouldn't avoid it for fear of having their production thrown for a loop.

Starting Pitchers

The WBC comes at a time of year when starting pitchers are focused on building up arm strength and finding their stride. Hence the reason why everyone freaks out so much about the WBC potentially ruining MLB starting pitchers. 

Because of this, starting pitchers are always going to be more worried about injuring themselves than other players. But should they fear a performance decline even if they survive the WBC?

Let's see. Here's a look at some notable starters from the 2006 WBC, with the requirements being 20-ish starts in 2005, multiple starts in the WBC and 20-ish starts in 2006.

The count: 11 pitchers, nine down, two even and zero up. 

In other words: Yikes.

There's little worth noting in regards to the even trenders. Johan Santana had a brilliant season in 2005, pitched well in the WBC and then had another brilliant season in 2006. It was no fluke either, as both his FIP (Fielding Independent Pitching)and xFIP (Expected Fielding Independent Pitching) stayed steady and the velocity records at FanGraphs show no glaring drop-off in heat.

Daniel Cabrera still wasn't very good in 2006, but he wasn't much worse than he was in 2005. FanGraphs velo records show Cabrera did lose some velocity, but his bigger issue in 2006 was a huge spike in walks. However, he helped himself offset that by striking out more hitters (FanGraphs).

Ronald Martinez/Getty Images

Clemens didn't pitch in the majors until June following the 2006 WBC.

Among the downers, the one guy who can be completely forgiven is Roger Clemens. To go from a 1.87 ERA to a 2.30 ERA is no crime, especially not when one does so after coming out of retirement.

Just as Clemens was himself following the 2006 WBC, the same can really be said of Joel Pineiro and Odalis Perez. They were coming off lousy seasons in 2005 and had lousy seasons again in 2006. 

Pineiro saw his strikeouts decrease, his walks increase and his ERA, FIP and xFIP increase across the board (FanGraphs). He'd been on thin ice for two years before 2006, and it finally broke even despite his strong showing in the WBC. It's possible he overexerted himself, but the velocity charts show no glaring changes in Pineiro's heat.

Perez had experienced a sharp decline in 2005 that coincided with left shoulder problems, and he watched his strikeouts decrease and his BABIP skyrocket in 2006 (FanGraphs) after getting rocked in the Classic. Records show he barely threw his fastball, which had lost some zip the prior year.

Rodrigo Lopez would seem to be in the same boat as Pineiro and Perez, but he didn't pitch as poorly in 2006 his 5.90 ERA would indicate. His walk rate stayed steady while his strikeout rate increased, making the BABIP spike he suffered in 2006 the primary culprit for his struggles (FanGraphs).

Same goes for Javier Vazquez. His control wasn't as sharp in 2006 as it had been in 2005, but it was still very good. All the same, he ended with an ERA much higher than both his FIP and xFIP (FanGraphs). He was likely done in by his move to the American League rather than his pitching.

Ditto Esteban Loaiza, who also moved from the NL to the AL in 2006. He was done in by a significant decrease in strikeouts that didn't come with a decrease in BABIP. With more balls in play finding holes, it's no wonder his ERA, FIP and xFIP all rose (FanGraphs). 

Jake Peavy also deserved better than his ERA in 2006, but not by much. He didn't have his same control in 2006, and his FIP and xFIP increased along with his ERA (FanGraphs). Though he didn't lose any zip off his fastball, there's enough to wonder if pitching in the WBC took its toll.

Freddy Garcia experienced a similar regression in 2006. He didn't alter his walks or strikeouts all that much, but his ERA skyrocketed along with his FIP and xFIP (FanGraphs). The velo records show there was some lost velocity in his case, which surely didn't help. Also, pitching in the WBC after pitching 228 innings in 2005 and then 21 more in the postseason probably wasn't wise.

Jed Jacobsohn/Getty Images

The magic wore off for Willis in 2006.

And then there's Dontrelle Willis, who didn't resemble the pitcher who nearly won the NL Cy Young in 2005 after struggling in the WBC. 

Willis' control was his biggest issue in 2006, as his walk rate went way up after bottoming out at 2.09 per nine innings in 2005 (FanGraphs). He showed warning signs in the tournament, walking six in his 5.2 innings of work while also giving up 10 hits. The hits kept coming in 2006, as his BABIP went back up over .300 after finishing at .282 in 2005.

So of these 11 cases, Peavy, Garcia and Willis stand out as reasonable cautionary tales of pitching in the WBC. As far as fellow starting pitchers are concerned, that's three too many.

Now then, on to the 2009 WBC.

You'll notice the small sample size here. That's because relatively few major leaguers made multiple starts in the WBC and not all of them survived to make 20 starts in 2009. Peavy and Daisuke Matsuzaka are two notables who were undone by injuries.

Regardless, the final count: six total pitchers, four up and two down.

However, the first thing you'll immediately notice about the four up trenders—Vazquez, Ian Snell, Jonathan Sanchez and Ted Lilly—is that they really had nowhere to go but up. None of the four had an ERA below 4.00 the previous season in 2008.

Kevin C. Cox/Getty Images

Vazquez finished in the top five of the Cy Young voting in 2009 for the first time in his career.

Vazquez improved the most in going from 4.67 to 2.87, and an improvement like that was in the cards for two reasons. One is the fact that he moved back to the NL in 2009, and the other is the fact that his FIP and xFIP were significantly lower than his ERA in 2008 (FanGraphs). His turnaround thus can't be completely chalked up to his strong showing in the WBC, but it may have helped him get on a roll.

Sanchez was due for an improvement based on his FIP and xFIP showings in 2008 as well, as both figures said he deserved a lot better than a 5.01 ERA (FanGraphs). He improved not to much because of better control in 2009, but because of a higher strikeout rate and a lower BABIP. 

Lilly benefited from two things in 2009: fewer walks and fewer homers. His HR/FB rate got back down to where it was in 2007 after spiking in 2008, and his walk rate plummeted to 1.83 per nine innings (FanGraphs). A surprising turn seeing as how he gave up three homers and three walks in the WBC.

As for Snell, his ERA improvement in 2009 was a fluke. He struck out fewer and walked more than he did in 2008, making his success largely a result of his .291 BABIP and 7.5 HR/FB rate (FanGraphs). It's possible that he overexerted himself in the WBC, but more likely that he stunk to begin with.

While we're on the topic of flukes, Armando Galarraga was never as good as his 3.73 ERA in 2008 indicated. His FIP and xFIP were both in the 4.00s, and he never had a real shot at repeating his .236 BABIP (FanGraphs). His struggles in 2009 were a sort of correction.

Roy Oswalt also falls into the fluke category. His ERA rose in 2009, but his FIP and xFIP stayed relatively steady in the 3.00s (FanGraphs). He was a victim of a high BABIP, and also of many injuries to his right hand and lower back. That would be a warning sign if not for the fact that Oswalt was always dealing with this or that when he was playing.

Thus, there are no real legit cautionary tales in this six-pack of pitchers. If there is a cautionary tale, it's in the fact that there are only six pitchers to speak of. It's also not overly encouraging that it's debatable if any of the six truly benefited from pitching in the WBC.

Regardless, the combined count for starting pitchers is 11 down trenders, four up trenders and two even trenders.

We can talk all we want about flukes and whatnot, but that's not an encouraging sight for would-be WBC pitchers. Factor in the hurlers who weren't discussed here due to injuries, and I'd say starting pitchers have enough evidence to play it safe by staying out of the WBC and at spring training.

Relief Pitchers

If relievers have an advantage on starting pitchers in the WBC, it's that they're not being asked to do anything out of the ordinary. They're coming in to throw an inning or to get a couple batters out, which is what they tend to do both in spring training and pretty much at all times.

By this logic, relief pitchers ought to fare well from one year to the next with the WBC in between. 

Let's see. Here's a look at a sample of relievers from the 2006 WBC, all of whom made 40ish appearances in 2005, multiple appearances in the Classic and over 40 appearances in 2006.

The count here: four up, four down and two even.

It's all too fitting that Scot Shields would be one of the even trenders. He was one of baseball's most consistent relievers in his day, and it was more of the same for him in 2006. He saw his strikeouts decline, but he offset the decline with a decrease in walks (FanGraphs).

Kiko Calero, meanwhile, wasn't much of a strikeout artist before 2006 or in the WBC, but he became one in 2006. His K/9 jumped from 8.41 to 10.40, which more than helped offset a spike in walks (FanGraphs). The rise wasn't necessarily a fluke seeing as how Calero had been a solid strikeout reliever in 2003 and 2004.

As to the down trenders, Fernando Rodney wasn't really as good as his 2.86 ERA in 2005 would indicate, as both his FIP and xFIP were in the high 3.00s (FanGraphs). His wildness in the WBC (three walks in 4.2 innings) turned out to be a precursor to a high walk rate that hurt him in 2006.

Jed Jacobsohn/Getty Images

Right-handers had a 1.033 OPS against Romero in 2006, yet he faced more righties than lefties that year.

J.C. Romero was also due for a decline in 2006 after posting an ERA way lower than his FIP and xFIP in 2005 (FanGraphs). You can only survive so long with a BB/9 over 6.0 and a BABIP well under .300. Sure enough, Romero's walk rate stayed high, his strikeout rate declined and his BABIP soared in 2006 to result in his 6.70 ERA. 

The other two down trenders can be forgiven. It was never going to be easy for Huston Street to repeat his 1.72 ERA, and he actually improved his FIP and xFIP in 2006 (FanGraphs). Salomon Torres did the same (FanGraphs).

As to the up trenders, Joe Nathan and Francisco Rodriguez got more awesome than they already were. Nathan had an even bigger K/BB than the one he had in 2005 to thank for his success in 2006, as well as an improvement on his already impressive HR/FB (FanGraphs). K-Rod also allowed fewer dingers, and he decreased his walks while keeping his strikeouts steady (FanGraphs).

Jorge Julio wasn't as sharp as either Nathan or K-Rod in 2006 in regards to walks or homers, but he did drastically increase his strikeout rate (FanGraphs). He teased that he would do so in the WBC with five strikeouts in 3.1 innings.

Duaner Sanchez didn't improve his walks or strikeouts in 2006, but he did get more ground balls and keep more balls from going over the fence. Because his BABIP also declined, he was able to enjoy a fine season before it came to an early end thanks to a July car accident (FanGraphs). 

So of the 10 pitchers profiled here, only Rodney and Romero really suffered in 2006 following their appearances in the WBC. Everyone else did alright, which is a good sign for relievers who might consider the WBC in the future.

But how about the 2009 WBC?

The count here: five down, four up and one even.

Matt Thornton is the Scot Shields of this sample size, as he was as steady as any reliever in the majors between 2008 and 2010. His numbers barely budged in 2009 thanks largely to consistent walk and strikeout rates, both of which remained top-notch (FanGraphs). 

Among the down trenders, Brad Ziegler is most easily forgiven because he was never going to sustain his 1.06 ERA from 2008. The numbers suggest he actually pitched better in 2009, as his strikeout rate increased and his FIP and xFIP both improved (FanGraphs). His WBC issues didn't linger.

J.P. Howell, Joel Hanrahan and John Grabow can also be forgiven. Howell's ERA rose, but it still stayed under 3.00 thanks to an increase in strikeouts and a steady BABIP (FanGraphs). Hanrahan kept his strikeout and walk rates steady in 2009, but was crushed by an unreasonably huge BABIP spike (FanGraphs). Grabow also paid the price for a big BABIP spike (FanGraphs).

Elsa/Getty Images

In retrospect, the 2009 WBC looks like the beginning of the end for K-Rod.

K-Rod is a different story. He had an epic season in 2008 and showed well in the WBC, but he struggled in 2009 thanks to regressions in his walks and strikeouts (FanGraphs). PITCHf/x data shows that his fastball wasn't as effective in 2009, which could, in theory, be chalked up to the WBC.

While K-Rod was busy declining as a closer, Jonathan Broxton and Heath Bell were establishing themselves as shutdown closers. Broxton used a 13.5 K/9 to rack up a 2.61 ERA that his FIP and xFIP say actually should have been better (FanGraphs). Likewise, Bell drastically increased his strikeout totals in his first year as a closer (FanGraphs).

Pedro Feliciano also deserved his fine year in 2009. He cut way down on walks, increased his strikeouts and also slightly improved his ground-ball rate, resulting in improvements across the board in ERA, FIP and xFIP (FanGraphs).

LaTroy Hawkins, on the other hand, was lucky. His ERA nosedived, but not his FIP and xFIP (FanGraphs). Since his BABIP stayed steady and his HR/FB rate went way up, it's a mystery how he was able to maintain a 2.13 ERA in 2009.

So just like with the 2006 WBC sample, there are only two pitchers here who went through legit issues in 2009: K-Rod and Hawkins (despite what his ERA said). That makes the big picture out for relievers to be largely positive, as there are only a couple cautionary tales to speak of out of a group of 20 pitchers. Most of the others carried on as usual, as prone to good and bad luck as the next reliever.

Relievers thus shouldn't worry too much about the WBC. It's not as scary for them as it is for starting pitchers. 

Note: World Baseball Classic stats courtesy of tournament's official website. All other stats from Baseball-Reference.com unless otherwise noted. Injury notes from Baseball Prospectus.

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