Regression (n.) - a trend or shift toward a lower or less perfect state.
A lot of guys have started the 2013 season on fire, but many of them will inevitably fizzle out.
Using advanced metrics like BABIP, xFIP, wRC+ and common sense, here is a list of the 15 players most likely to experience a significant decline in the upcoming weeks.
Don't worry if you don't know what any of those acronyms mean, as I've included a brief description of many a baseball statistic on the next slide.
*All stats and stat definitions in this piece are courtesy of FanGraphs.com and are accurate as of the start of play on Tuesday, April 23.
It's great to back up arguments with both traditional and advanced statistics, but what good are they if you have no idea what they mean?
If you consider yourself a seasoned sabermetrician, go ahead and jump straight to the next slide. But for those of you who enjoy baseball despite a degree in something other than statistics, here's a quick crash course to help you through the next 15 slides.
Earned Run Average (ERA): The number of earned runs allowed per nine innings pitched. One of the more basic statistics in baseball.
Batting Average (AVG): Hits divided by at-bats. Far from rocket science.
Slugging Percentage (SLG): In a nutshell, it's a weighted batting average. Singles count as one hit, doubles as two hits, triples as three hits and home runs as four hits.
Expected Fielding Independent Pitching (xFIP): Essentially, what a pitcher's ERA should be. It takes fielding out of the equation, focusing on home runs, walks, strikeouts and hit batters. Typically used as a means of predicting future results under the theory that ERA should eventually converge with xFIP.
As an example, Kansas City Royals reliever Kelvin Herrera has an ERA of 5.79 but an xFIP of 2.74, meaning his ERA should drop considerably over the coming weeks and months. Either that or he'll be pitching in the minor leagues soon.
Batting Average on Balls in Play (BABIP): Basically the inverse of xFIP, BABIP focuses only on balls in play by removing strikeouts and home runs from the equation. A high BABIP means a batter has been fortunate in avoiding fielders when making contact.
Generally, a batter's BABIP will be slightly better than his batting average, so large differences between the two can be considered an indication of future success or regression.
Left On-Base Percentage (LOB%): The percentage of base runners that a pitcher strands on base over the course of the season. The league average is roughly 72 percent. Pitchers with a higher percentage should be considered luckier than the ones with a lower percentage, and it should be expected that pitchers will finish the season somewhere in the vicinity of 72 percent.
If a pitcher has a low ERA and a high LOB%, beware of regression.
Weighted Runs Created Plus (wRC+): Calculates the number of runs that a player is worth to his team and then grades on a curve. 100 is the league average, but players like Barry Bonds have been known to score in the mid-200s in MVP-caliber seasons.
2013 ERA: 1.03
2013 xFIP: 3.44
Career ERA: 4.26
With Jamie Moyer and Livan Hernandez out of the picture, Paul Maholm has taken the reins as one of the premier junkball pitchers in the league.
The velocity on his fastball is down more than three MPH from where it was in 2008, and he has already thrown a curveball this season clocked at 57.8 MPH. Just to put that under-handed lob in perspective, I was throwing 63 MPH fastballs at the age of nine—and I was hardly a prodigy.
However, Maholm's current numbers are neither sustainable nor anywhere near his career averages. His lowest ERA in any given season is 3.66. His K/9 of 8.54 is a far cry from his career rate of 5.71. Also, his HR/FB ratio of 5.0 percent is less than half of his career rate of just over 10 percent.
It's hardly breaking news that he's not going to finish the season with an ERA of 1.03, but once opposing hitters get into midseason form and are able to spot a junkball a mile away, his ERA will gradually creep back towards 3.50.
2013 BABIP: .419
AVG (2013 / Career): .339 / .281
wRC+ (2013 / Best Career Season): 156 / 123
Not only is Denorfia off to an unusually hot start, but he'll be returning to his role as either the fourth- or fifth-best outfielder in San Diego now that Carlos Quentin has returned from his suspension.
Even if he finds regular playing time, his batting average is 46 points higher than in any previous season. Also, a .419 BABIP is completely unreasonable for someone who only homers or strikes out in one out of every six at-bats.
2013 ERA: 2.08
2013 xFIP: 4.46
Career ERA: 4.22
In 2012, we finally saw a home run rate that makes sense for a guy like Travis Wood.
Despite a ratio of 1.91 fly balls for every ground ball, Wood somehow survived his two years in Cincinnati allowing just 0.82 HR/9. He was extremely fortunate and still had an ERA of 4.18.
He then moved from one hitter's park to another, getting destroyed by the long ball in Chicago at a rate of 1.44 HR/9 in 2012. Thus far in 2013, that number is all the way down to 0.35 HR/9, explaining both his low ERA and high xFIP.
When the wind starts blowing out to left field in Wrigley, expect Wood's ratios to increase as well.
2013 BABIP: .451
AVG (2013 / Career): .366 / .289
wRC+ (2013 / Best Career Season): 212 / 150
Shin-Soo Choo is off to a torrid start in his first year with the Reds.
Virtually all of his batting statistics are better than in any other season. His walk rate is higher, his strikeout rate is lower and his BABIP is 81 points higher than his previous career high. As a result, through 20 games he's getting on base 30 percent more often than he ever did before.
There's something to be said for a change in scenario and a change in the batting order. Choo spent the bulk of his time in Cleveland batting in the heart of the order, being "protected" in the lineup by guys like Travis Hafner, Matt LaPorta, Shelley Duncan and Russell Branyan.
Now that he's batting leadoff in front of Joey Votto, Brandon Phillips and Jay Bruce, it's reasonable to assume that pitchers aren't saving their best stuff for him in the way they would have over the past five years.
Still, a .451 BABIP is just plain silly. No one has finished a season with a BABIP of .400 or better in the past decade, and Choo's best full-season BABIP before this year was .370. He'll regress a bit, but maybe not as much as some of these other guys.
2013 ERA: 1.90
2013 xFIP: 4.35
Career ERA: 4.66
I would love to reference Slowey's 2012 numbers, but there are none. After five disappointing seasons with the Twins, he couldn't even crack into the majors last year.
That alone should be cause for concern of regression on a 1.90 ERA. It should also be concerning that he's only owned in 1.3 percent of fantasy leagues despite the hot start.
No one is buying it.
In his career, Slowey has allowed at least 1.21 HR/9 in each season, but is sitting at just 0.76 HR/9 thus far in 2013. As a result, his LOB% is at 91.9 percent despite never finishing a season with a clip better than 74.1 percent.
Pitching in that canyon in Miami might help keep his HR numbers lower than usual, but he'll still give up more than his fair share of extra-base hits. It's only a matter of time.
2013 BABIP: .459
AVG (2013 / Career): .392 / .277
wRC+ (2013 / Best Career Season): 178 / 130
Either it took Torii Hunter 36 years to figure out the game of baseball, or he's having an incredibly lucky stretch since the beginning of 2012.
Hunter was near the top of the BABIP leaderboard last year, and he's back there again thus far in the current campaign. In 2012, his strikeout rate was over 20 percent for the first time in a decade, but he also batted over .300 for the first time in his career.
Here are two things that don't add up, though.
Hunter is swinging at 38.3 percent of pitches outside of the strike zone—a full 10 percent higher than his career rate of 28.1. However, he's making contact on 83.8 percent of swings, which is seven percent better than the 76.8 mark he's tallied in his career.
Hunter is swinging at worse pitches and hitting them more often for one of the best BABIP numbers in the league. If that doesn't reek of dumb luck, I'm not sure what does.
2013 ERA: 1.42
2013 xFIP: 4.09
Career ERA: 4.00 (includes AA and AAA stats from 2011 and 2012)
This is only Corbin's second year in the majors, so it's a little unfair to judge him in the same historic manner that most of the other guys on this list are being assessed.
Having said that, it's not as though he was blowing guys away in the minors, and he wasn't even touted as a better prospect than Wade Miley or Trevor Bauer. Between three levels of the Diamondbacks' organization, he had an ERA of 4.00, a BB/9 of roughly 2.3 and a BABIP of .330.
Once he reached the big leagues at the end of April 2012, he was roughed up for 1.18 HR/9 and actually ended up with an ERA nearly a full run higher than his xFIP.
Through three starts in 2013, his walk rate is at a career high and his strikeout rate at a career low. However, the home runs and BABIP have decreased considerably, and the LOB% is nearly 92 percent.
Pitching half of his games in Chase Field, it's safe to assume the home run rate will increase to or beyond last year's total, especially if the strikeout rate doesn't.
2013 BABIP: .418
AVG (2013 / Career): .361 / .250
wRC+ (2013 / Best Career Season): 194 / 144
Between injuries and ineffectiveness, Lowrie has never before been an everyday type of guy. Though he's played in all 20 games for Oakland this season, he has failed to reach 100 games played in any of his other five seasons in the big leagues.
The optimist would say his career numbers are so low because he's never had a chance to get into a proper groove. He's only once batted better than .260 and only once had a BABIP of better than .300. Now that he's getting at-bats every day, he's seeing the ball better and can sustain these numbers.
Unfortunately, we're not looking at the half-full side of the glass today.
Fool me once, shame on you; have a stint on the DL in five consecutive seasons, also shame on you. Some bodies just weren't meant to withstand the rigors of a full MLB season.
Even if he breaks that trend and stays healthy, it's difficult to figure out Lowrie's potential upside. With the exception of Yoenis Cespedes, Oakland is where home run hitters go to die. Lowrie was never exactly a slugger anyway, homering in just one out of every 32.8 at-bats in the friendly confines of Boston and Houston.
If previous years are any indication, he'll be lucky to hit a dozen home runs while batting .275 with maybe three stolen bases.
2013 ERA: 0.90
2013 xFIP: 3.21
Career ERA: 3.92
Between torn fingernails, pulled hamstrings, stress fractures and esophagitis, Buchholz has missed nearly half of his potential starts while on the disabled list. He's only made more than 16 starts in two seasons, posting a spectacular 2.33 ERA in 2010 and a much less impressive 4.56 ERA in 2012.
In the great season he had a HR/FB ratio of 5.6 percent, but that number ballooned to a more average 13 percent in 2012.
The real question is: Which Buchholz is going to show up this season? Thus far, he's combined the BABIP of 2007 with the K/9 of 2008, the xFIP of 2009, the home run rate of 2010, the LOB% of 2011 and the BB/9 rate of 2012.
He's done each part of his 2013 season in a previous year, but never altogether in one Cy Young-worthy season. He could end up having a very impressive season and still regress considerably from his current rates. A sub-1.00 ERA and a K/9 rate two strikeouts better than the previous four seasons is hardly sustainable.
At-Bats per HR in 2013: 8.9
At-Bats per HR in Career: 26.5
2013 AVG: .290
Career AVG: .235
Only once in his 10-year career has John Buck batted better than .247, and only once has he had a wRC+ of 100 or better. Both of those things happened in his one year with the Blue Jays in 2010, in which he averaged a home run in every 5.9 games.
Through 10 percent of the 2013 season, he is destroying career averages with one home run every 2.4 games and a wRC+ currently 44 points higher than he has finished any other season. Buck is slugging 172 points better than he did in that career year in 2010.
If you think guys can suddenly put together an MVP-caliber season after years of evidence suggesting otherwise, allow me to point you toward the month-by-month splits of Ubaldo Jimenez's 2010 season.
Even if Buck regresses to match his career-best totals, he would bat .278 and slug .458 the rest of the season, which are roughly equal to the numbers Ryan Doumit put up last season. Suffice it to say, Ryan Doumit was not an MVP in 2012.
2013 ERA: 1.25
2013 xFIP: 5.26
Career ERA: 4.30
By this point, we know what we expect from Jake Westbrook, right?
Over the past three seasons, he's averaged six innings pitched, seven hits, three earned runs, two walks and four strikeouts per start. He'll give you a quality start more often than not, but don't expect any miracles.
The bizarre thing about Westbrook's low ERA in 2013 is that he's allowed 32 baserunners in 21.2 innings pitched, but only three of those guys have come around to score. Allowing nine percent of your baserunners to score and allowing zero home runs over the course of three starts is unusual to say the least.
Also bizarre is that he got off to a similarly hot start last season, finishing the month of April with a 1.30 ERA and a ground ball rate of 71 percent. He followed it up with 33 earned runs in his next 50.2 IP to get his ERA back up to a more typical 4.27.
Expect similar results over the next month.
2013 BABIP: .468
AVG (2013 / Career): .407 / .276
wRC+ (2013 / Best Career Season): 183 / 119
Having a high BABIP isn't particularly out of the ordinary for Chris Johnson. Among all qualified players, he ranks eighth in BABIP from 2010 to 201212 at .351.
However, .468 is a far cry from .351. BABIP can definitely skew a bit high for people who strike out a lot, but no one is getting on base almost half of the time they make contact with the ball.
That number—along with his .407 batting average—is going to drop like a rock in the coming weeks, possibly decreasing his value far enough to enter into a platoon situation with Juan Francisco at third base.
With the return of Freddie Freeman, manager Fredi Gonzalez has said Johnson will be the everyday third baseman. We'll see if that holds true, as he would bat just .260 the rest of the way if he drops back down to his career batting average.
2013 ERA: 1.29
2013 xFIP: 3.37
Career ERA: 4.26
Villanueva has had an atypical career, bouncing in and out of the starting rotation in each of the past seven seasons for Milwaukee and Toronto. He has been essentially the definition of a replacement level player, recording a WAR between 0.1 and 0.5 in six of those seven seasons.
Whether in the rotation or in the bullpen, what has been consistent with Villanueva is a high BABIP and a worse-than-average ERA.
Neither of those things has been remotely true through his first three starts of this season. His ERA is almost three full runs below his career average and his BABIP is 100 points lower than what it was from 2006 through 2012. His LOB% is a slightly unsustainable 100 percent, and his K/9 is substantially lower than his career rate.
Literally the only thing about his stat line that doesn't scream "Regression!" into a megaphone is a career low in BB/9, but let's go ahead and assume that will also regress rather than foolishly believing it might be an indication of a prolonged improvement.
2013 BABIP: .419
AVG (2013 / Career): .391 / .258
wRC+ (2013 / Best Career Season): 243 / 126
Davis put up some pretty solid numbers last season, batting .270 with 33 home runs. It's not as if this came completely out of nowhere.
Through 19 games in this season, his slugging percentage is 327 points higher than it was in 2012, and he's on pace to more than double his weighted runs created from his best season to date.
To an extent, we can write it off as predictable progress. He just turned 27 years old and this is only his second year in the majors as a full-time starting player. It's possible he's just now starting to reach the peak of his potential.
But nobody slugs .828. Nobody except for Barry Bonds, and I will do Chris Davis neither the honor nor the dishonor of comparing him to Barry Bonds. With the exception of Bonds, the highest slugging percentage in a single season over the past decade was Albert Pujols' mark of .671 in 2006.
Pujols has been a slugger from Day 1, though. In his first 10 seasons in the league, his lowest slugging percentage was .561.
Chris Davis is no Albert Pujols. He may have something close to the same amount of power, but Pujols consistently batted .330 while striking out in less than 10 percent of his plate appearances. Davis' numbers are more like .260 and a 30 percent strikeout rate.
A much more appropriate comparison for Chris Davis would be Adam Dunn, who has a career BABIP of .286 and an average wRC+ of 123. The homers are for real—he could definitely hit 40—but the peripheral numbers are not.
2013 ERA: 1.69
2013 xFIP: 3.47
Career ERA: 3.16
There are just two things you need to know about Hisashi Iwakuma before you go sprinting to your fantasy team to trade him away as quickly as possible.
1) He currently has a LOB% of 100 percent. While it's definitely possibly to deviate from the league average of 72 percent, the best percentage by any pitcher in any of the past three seasons was 82.7 by Cole Hamels, Roy Halladay and Jeremy Hellickson. Eventually those baserunners are going to start scoring on something other than home runs.
2) He currently has a BABIP against of .119—the lowest of any qualified pitcher in the Majors. This means that only one out of every nine balls in play is falling in for a hit. The league average is typically around 30 percent, with the lowest of 2012 being the .241 mark shared by Jered Weaver and Ervin Santana.
Considering he's only striking out six batters per nine innings pitched, there are a fair number of balls in play when Iwakuma is pitching, and he will inevitably regress towards league averages before much longer.