With the playoff races shaping up and four of Major League Baseball's six divisions still up for grabs, every team left in contention has an X-Factor that could potentially drive them into October or send them home for an early winter.
Generally speaking, an "X-Factor" is simply a variable posing a great chance at having a significant impact on an outcome. In this case, it could be an individual player, a tendency or even an entire aspect of one team. Every team has at least one of the above—and it could make or break their season.
There are 13 teams still vying for a trip to the playoffs, although some are closer to the fight than others.
Here is every contender's biggest X-factor down the stretch.
The Arizona Diamondbacks will go only as far as Justin Upton is able to carry them.
After a down 2010 season that culminated with trade rumors swirling around Upton, the 24-year-old has fired back to have the best season of his career. He should smash his career marks in home runs, RBI and stolen bases, and his year-over-year OPS has gone from .798 to .909.
The D-Backs currently have a six-game lead over the San Francisco Giants in the NL West. Their rotation has been consistently solid all season long, and their bullpen has been clutch—leading all of Major League Baseball with 47 saves.
Their issue is a lack of consistency on offense surrounding Upton, while the team is near the bottom in baseball with a .248 batting average.
So far this season, the D-Backs have used the long ball to offset their lack of consistency. That won't work against the Giants, nor will it work against any other team vying for a playoff spot—unless, of course, Upton continues to lead the way.
The San Francisco Giants traded for Carlos Beltran for one reason and one reason only: to give them a much-needed boost on offense.
While Beltran has increased his average with the Giants to .286, he has only one home run, two doubles and four RBI since joining the club near the end of July. That's not the kind of production they were hoping for when they gave up Zach Wheeler for his temporary services.
The "Jekyll and Hyde" known as the Giants' offense and defense is almost amazing. Their 3.14 ERA is second in baseball and top in the National League. However, their 454 runs are the worst mark in all of baseball, while their .235 team batting average and .300 on-base percentage are the worst in the NL.
The only way the Giants stand a chance at capturing the NL West title with an opportunity to defend their crown is if the offense begins to step up in a big way. That begins and ends with Carlos Beltran.
While "consistency" may seem vague in describing what a contender needs to do down the stretch, anyone who has followed the Milwaukee Brewers over the last five years knows there is no better word to describe their X-Factor.
When the Brewers are pounding the ball, their pitchers are giving up a lot of runs. Yet, when their pitchers are shutting down opponents, the offense forgets to show up and they put only a couple runs on the board.
For example, this past June, while the Brewers hit more home runs and scored more runs than in any month of the season, their pitchers had by far their worst ERA out of any month this year. August is the first month they've been rather good on both sides of the ball.
No team in baseball is as consistent in their inconsistencies as the Brewers, and to keep the Cardinals from catching them while capturing their first division title since 1982, they're going to have to stabilize the ship.
Let's face it: at this point, the St. Louis Cardinals don't even belong on this list. They are currently 8.5 games behind the hottest team in baseball, and the Brewers show no signs of letting their grip on the NL Central slip away.
For the Cardinals to even get back in the race, they'd have to go on an insane hot streak while the Brewers decided to monumentally collapse. At this point, if the Brewers don't win the division, it would be up there with one of the worst collapses in Major League Baseball history.
In reality, their pitching is mediocre at best, and they scored a lot of runs earlier in the season when they were getting on base a lot—although, their run production in August is by far the worst of the season, and all of their peripherals are quickly dropping.
The Cards have a key series in St. Louis against the Brewers next week. If they don't take all three games, they're probably as good as done.
The Atlanta Braves currently hold a nine-game lead in the NL Wild Card race while trailing the Philadelphia Phillies by seven games in the NL East. Simply put, the Braves are all but a lock to reach the playoffs for the second year in a row.
The only thing that could stop them from reaching the NLDS, while certainly hurting their chance to be able to compete in the postseason, is whether or not Tommy Hanson can rejoin the rotation down the stretch and regain form.
Hanson has been shut down since August 7th with a slight tear in his rotator cuff, although manager Fredi Gonzalez is hopeful he will return in September.
Fellow pitcher Jair Jurrjens has struggled since coming back from an injury and has allowed five or more runs during four of his last seven starts. This leaves Tim Hudson to anchor a rotation with Brandon Beachy and Derek Lowe—not a very fearsome trio and, at this point, well below any other NL playoff hopefuls.
The Braves need Hanson back—and soon.
Injuries have plagued the Philadelphia Phillies this season, yet they still sit comfortably atop the NL East with the best record in all of Major League Baseball.
Their latest blow may hurt them most of all, as former NL MVP Jimmy Rollins is sitting on the DL with a strained groin. His return date is in question.
This is a huge blow to the Phillies, who will miss his bat in the lineup and his defense in the field. The left side of their infield just happens to be where the Phillies have the least depth, and Wilson Valdez will not be able to provide the offense or defense they received from Rollins.
Hunter Pence has helped ignite a stagnant Phillies offense since his acquisition in July, but losing Rollins for an extended period of time could put them back at square one.
The Texas Rangers can put up runs with any team in the league. Although Nelson Cruz was just lost for a few weeks, the return of Adrian Beltre in the coming days should prevent the Rangers from missing a beat on offense.
Their main concern is pitching. More specifically, it's their rotation behind staff ace C.J. Wilson. While the Rangers revamped their bullpen before the trade deadline, the starting rotation lacks a bona fide No. two or No. three starter.
Colby Lewis has allowed 12 runs over his last two starts, Matt Harrison has allowed 17 runs over his last 14.2 innings and Alexi Ogando has allowed 18 runs over his last 20 innings. Their No. 5 starter, Derek Holland, has pitched the best of the four, yet he's still allowed 18 runs over his last 22.1 innings.
It comes as no coincidence that the Rangers have seen their seven-game lead in the AL West cut in half over the last two weeks.
With Jered Weaver, Dan Haren and Ervin Santana forming a formidable trio for the red-hot Los Angeles Angels, the Rangers rotation needs to get it together quickly if they want to wrap up a second consecutive division title.
I was surprised Wells didn't swing at this pitch.
While Jered Weaver and Dan Haren lead a dominant trio atop of the Los Angeles Angels' rotation, they can't win games if they don't put runs on the board.
Vernon Wells is reminding us all that he holds possibly the worst contract in Major League Baseball history, and you have to wonder how badly the Angels regret acquiring the slugger over the offseason.
Wells is currently hitting .215 with 18 home runs, along with a career-worst 79 OPS-plus. That's not what the Angels were hoping for, and it surely won't help them reach the postseason.
The Angels have a great mix of young players and seasoned veterans, but sadly, their playoff chances may hinge on whether or not Wells can awaken is stagnant bat.
No contending team has been devastated by injuries this season more than the Cleveland Indians.
Soon-to-be former franchise player Grady Sizemore has appeared in only 61 games this season, while Travis Hafner has played in only 82. Both are currently on the DL with their season in doubt. Shin-Soo Choo just returned from a long DL stint as well and has only suited up for 84 games so far.
You can also add pitchers Carlos Carrasco and Josh Tomlin to the list of important pieces who are currently on the DL.
While injuries have definitely taken their toll on the Indians, it's still impressive that they've been able to stick around as long as they have. They are currently only six games back with an outside chance of making a run.
For that to happen, the Indians need to get some players back from the DL soon while staying injury-free down the stretch.
Swing and a miss
Yes, I do realize that at this point Adam Dunn is only getting in the lineup two or three times a week. With a .163 average and only 11 home runs on the season, it's hard to blame Ozzie Guillen for keeping the burly slugger on the pine.
However, for the Chicago White Sox to cut into their six-game deficit in the AL Central, they need their $56 million home run hitter to start producing at the plate and earn his spot back into the everyday lineup.
After a very shaky April, the White Sox's starting rotation has shown steady improvement since the beginning of June, with John Danks and Gavin Floyd finally resembling their old selves.
In my opinion, the White Sox are by far the most talented squad within the division. At this point, they just need a big bat in between Paul Konerko and Carlos Quentin in the lineup to give their pitchers more run support.
Justin Verlander would be the anchor of almost any rotation in Major League Baseball. Unfortunately for him, the rest of the Detroit Tigers' rotation has continued to underachieve this season. That is, aside from deadline acquisition Doug Fister.
Acquiring Fister may go down as the best trade made at this years deadline. After a couple of rocky outings to begin his Tigers career, Fister has held opponents to two runs over his last 21.2 innings and currently holds a 2.97 ERA since joining the team.
For the Tigers to hold onto their six-game lead in the AL Central and to improve their chances of making some noise in the playoffs, they are going to need a bona fide No. 3 starter.
The Tigers had hoped Max Scherzer could be that man, yet the 27-year-old has been rather inconsistent this season and currently sits with a 4.52 ERA. The same goes for one-time top prospect Rick Porcello, who has continued to struggle against big league hitters. He currently sits with a 5.01 ERA.
With Verlander and Fister at the top of their game, the Tigers have the potential to be a very tough team heading into the postseason if one more arm can step it up.
The Boston Red Sox are in the same position as the Detroit Tigers, yet they have two legitimate staff aces atop their rotation in Jon Lester and Josh Beckett.
The Red Sox also boast one of the best offensive squads in Major League Baseball, so the only thing they're worried about at this point is having a No. 3 starter in place down the stretch and into the playoffs.
Clay Buchholz's injury has prevented the Sox from having a solid one-two-three in their rotation. Tim Wakefield is an innings-eater at best, and John Lackey is just plain awful.
The best bet to fill the No. 3 spot is Erik Bedard, who has pitched to a 3.46 ERA through his first five starts in Boston. The problem's are that he barely averages five innings per start and he definitely can't be counted upon to stay healthy.
Bedard has already made more starts this year than he has during any season since 2007. If he can stay healthy, the Sox can probably get by on five or six quality innings per start. But if Bedard goes down, they have no remotely reliable starter to step in as the No. 3.
The New York Yankees rotation appeared to be getting by over the seasons first few months, with Ivan Nova having a breakout season and Bartolo Colon seemingly having a career resurgence at 38 years old.
As the season has worn on, the Yankees have had to rely more on their offensive prowess while their pitching has struggled. Since August 1st, the Yanks' team ERA sits at 4.38. That's well above their 3.65 ERA on the season.
Colon has shown signs of wear as the season has progressed, with his ERA jumping by 0.30 points in August—a hefty increase this deep into the season. A.J. Burnett is as horrible as ever, and at this point, he may not even be considered for one of the three rotation spots in the postseason.
This leaves the Yankees with Freddy Garcia and Ivan Nova to follow CC Sabathia as their No. 2 and No. 3 starters heading into the playoffs. While some Yankees fans probably think the trio is as dominant as ever, any baseball-minded individual outside of the Bronx knows that this rotation will be in big trouble come October.
Jeffrey Beckmann is a MLB Featured Columnist for Bleacher Report. Follow Jeffrey on his new Twitter account for all of his latest work. You can also hear him each Friday at 1 pm EST on B/R Baseball Roundtable.