MLB 2011: Every Contender's Biggest Sleeper Prospect

Every team has a handful of prospects whose arrival in the major leagues is anxiously awaited by their fanbase, players who have the potential to not only be starters but be at the core of the franchise for years.

The same is true about September call-ups, as it is usually very clear which prospects have the best chance of stepping in with a promotion and making a significant difference in the team's playoff hopes. Inevitably, prospects emerge from the woodwork and far exceed expectations to make a big difference.

So here is a look at one sleeper prospect from each contender, the one player in line for a call up who is capable of surprising everyone and making a big difference in the playoff race.

Arizona Diamondbacks: Cole Gillespie

2011 Stats

.307/.414/.492, 12 HR, 78 RBI, 99 R, 24 SB

While the term prospect can be used loosely with the 27-year-old Gillespie, he could certainly make an impact down the stretch despite not being all that well known outside of Arizona.

He joined the team in 2009, coming over from the Brewers in the trade that sent Felipe Lopez out of town. With a good mix of power and speed, he could make a difference down the stretch as a pinch-hitter.

Atlanta Braves: Jairo Asencio

2011 Stats

44 Games, 3-2, 24 Saves, 1.39 ERA, 67 Ks, 51.2 IP

No doubt top prospects Randall Delgado and Julio Teheran get the attention as far as Atlanta pitching prospects go, but Triple-A closer Jairo Asencio has been fantastic this year and could make an already great bullpen even better in September.

The 27-year-old right-hander has made three different trips to the majors this year, most recently appearing on June 24th and while his 6.97 ERA over 10.1 innings is not great he has the potential to make a positive contribution in September.

Boston Red Sox: Ryan Lavarnway

2011 Stats

.289/.371/.557, 31 HR, 89 RBI, 73 R

Catching prospect Ryan Lavarnway is one of the Red Sox top young players, but he has a chance to steal some big at bats in the season's final months.

While the team has been pleased with the production of starting catcher Jarrod Saltalamacchia, but he has hit just .221 in August. So while Lavarnway is not a sleeper in terms of name recognition, he could make a far bigger impact that most people expect and start some important games for the Red Sox.

Chicago White Sox: Kyle Cofield

2011 Stats

1-2, 2.79 ERA, 25 Ks, 29 IP

The White Sox are short on minor league prospects at the moment, and especially short on pitchers, but right-hander Kyle Cofield who joined the team in 2010 in the deal that sent Scott Linebrink to the Braves could see some meaningful time in the bullpen.

After 15 appearances at Double-A this year after starting the season late, he was promoted Triple-A on August 31st and that could be a sign that he is on the path to Chicago. If he does end up with the big league team, he could be a useful arm seeing as he only has 29 innings under his belt this year.

Cleveland Indians: Zach McAllister

2011 Stats

11-3, 3.35 ERA, 1.185 WHIP, 121 Ks, 147.2 IP

Acquired in 2010 in the trade that sent Austin Kearns to the New York Yankees, Zach McAllister may very well be the best starting pitcher in the Indians farm system after they dealt much of their high-level talent for Ubaldo Jimenez.

He was called up last week, making his second start of the season after earning a spot start on July 7th, and he could be a part of the Indians rotation for the rest of the year as they try to mount a comeback and pass the Tigers. Not bad for at highest the third best pitching prospect the team had entering this season.

Detroit Tigers: Adam Wilk

2011 Stats

8-6, 3.35 ERA, 1.158 WHIP, 70 Ks, 99.1 IP

Starters Jacob Turner and Andy Oliver are cause for excitement in the Tigers not too distant future, but as far as 2011 is concerned left-hander Adam Wilk may make the biggest impact in September.

He had a five game audition earlier this season, pitching well in four of them and seeing his number ruined by a four-inning, four-run outing against the Rockies. Look for him to be a valuable lefty in the Tigers bullpen down the stretch.

Los Angeles Angels: Jeremy Moore

2011 Stats

.298/.331/.545, 15 HR, 66 RBI, 21 SB

Somewhat hidden in the large shadow cast by fellow outfield prospect Mike Trout, right fielder Jeremy Moore has quietly put together a very nice minor league career as he moved through the Angels minor league system.

He is certainly more big league ready than Trout, and he has not missed a beat in his first season at Triple-A. If any prospect is going to make a big impact offensively for the Angels down the stretch it will likely be Moore or no one.

Milwaukee Brewers: Cody Scarpetta

2011 Stats

8-5, 3.85 ERA, 1.376 WHIP, 98 Ks, 117 IP

While he may not be a sleeper to Brewers' fans, as he was ranked as their second-best prospect entering the year, Scarpetta is not exactly a household name as far as pitching prospects go.

The 22-year-old has spent the entire season at Double-A in this his fourth professional season, and enjoyed some success with an 8-5 record and 3.85 ERA over 23 starts. With the Brewers rotation somewhat set, he could help out in the bullpen but he will certainly be a contender for a rotation spot this coming spring or at some point in 2012.

New York Yankees: Andrew Brackman

2011 Stats

3-6, 6.19 ERA, 1.645 WHIP, 75 Ks, 93 IP

The towering 6'10" Andrew Brackman has had a roller coaster of a career with the Yankees so far in three pro seasons, as he has yet to live up to the lofty expectations that made him a first-round pick, but has shown flashes of dominance.

This year is no different, as he has a 6.19 ERA over 93 innings at Triple-A. However, he has been much better of late giving up just three runs in his last 17.1 innings with 17 strikeouts. He has the stuff to make an impact, and will likely be given a chance to do so.

Philadelphia Phillies: Michael Schwimer

2011 Stats

9-1, 10 Saves, 1.88 ERA, 86 Ks, 67 IP

The Phillies have some impressive pitching prospects in the lower levels, and at the major league level Vance Worley has been phenomenal in his rookie season. However, one pitching prospect who is largely overlooked is 6'8" right-hander Michael Schwimer.

Recently called up, Schwimer put together a dominant campaign at Triple-A this season with a line of 9-1, 10 saves, 1.88 ERA, 86 Ks, 67 IP. He should be a pivotal member of the bullpen down the stretch, and because he was called up before September 1st he could play a role in the postseason as well.

San Francisco Giants: Waldis Joaquin

2011 Stats

2-2, 3.31 ERA, 27 Ks, 49 IP

With Brian Wilson on the shelf, the Giants could use a boost in the bullpen and reinforcement could come in the form of burly right-hander Waldis Joaquin.

Joaquin has made brief appearances in the majors each of the past two seasons, and with a 3.31 ERA in 49 innings at Triple-A this season he will no doubt make another appearance. While he is not a closer candidate, he could be used early and often in a bullpen that has five guys that have already appeared in at least 55 games.

St. Louis Cardinals: Zack Cox

2011 Stats

.312/.368/.444, 13 HR, 68 RBI, 74 R

The Cardinals first-round pick last season, Cox is not a sleeper in the sense that he is not a big-time prospect but anything that he contributes this season would be somewhat surprising in his first pro season.

He has advanced to Double-A and has a combined line of .312 BA, 13 HR, 68 RBI, 74 R and seeing as he is already on the 40-man roster he could get a look this September and if he impresses there is no question he could push David Freese for the starting job next season.

Texas Rangers: Chad Tracy

2011 Stats

.251/.329/.451, 23 HR, 103 RBI, 71 R

Not to be confused with the former Diamondbacks corner infielder of the same name, Tracy has shown that if nothing else he has power, hitting 108 home runs in six minor league seasons.

He is 25 years old, and while he is not on the 40-man roster he is at the point where he doesn't have much else to gain from being in the minors. He is the only real power threat in the farm system and he could be a valuable bat off the bench while auditioning for a roster spot in 2012.