Five slumping hitters: Who will break out?

Every major league hitter goes through a slump. Sometimes it's a just a bad week here or there. Other times, it's a poor start or a slow month that may get established as part of a historical pattern. For example, when Mark Teixeira hit .136 in April of last season it was viewed as a traditionally slow start from Teixeira, who went on to hit .256 with 33 home runs and 108 RBIs. Sometimes though, slow starts stretch into extended slumps, which then develop into bad first halves and that's where we are with several hitters right now.

In some cases, it's hardly unexpected or inexplicable. Hanley Ramirez is hitting .205 but has been hampered by a nagging back injury. Adam Dunn is batting .185 with seven home runs but Dunn has been something of an all-or-nothing guy before. Other struggling stars like Ichiro or Hideki Matsui may just be aging. Some, like Aubrey Huff, may simply just be coming off career years or resurgent seasons. There are, however, other players whose extended slumps are more puzzling. Here are five players who have suffered some of the biggest OPS drops from last season and whose slow offensive starts may be the most baffling.

Dan Uggla, Braves

Worst slump of season: 5-for-63 (.079), May 16 to June 7.

According to the Elias Sports Bureau, Dan Uggla has had the biggest OPS decline of any player this season. Uggla's .877 OPS last season has plummeted to .566 after an 0-for-5 Thursday, a difference of .311 and well below his previous career-low of .805 in 2007. Uggla is batting .174/.244/.322, far below his career marks of .256/.341/.474. Another concern is Uggla's BABIP (batting average on balls in play), which has sunk from a career-high .330 last season to just .193. Uggla's groundball percentage is up to nearly 45 percent, by far highest of his career. He hit just .202 in April and followed with a .160 May, during which he managed only two home runs. From May 1 through June 15, Uggla hit .166 and slugged just .290. His Wins Above Replacement, a career-best 5.0 last season, is now -0.5, second-worst to only Orlando Cabrera among major league second basemen.

Shin-Soo Choo, Indians

Worst slump of season: 9-for-54 (.167), May 30 to June 14.

Choo's OPS has slid from .885 last season to .670. His 6.0 Wins Above Replacement last season is down to 0.8. Choo's season has actually seen a pair of lengthy slumps. He hit just .207 (17-for-82) from April 1 to April 24, followed by his most recent May 30-June 14 skid, during which he went without a home run and had just one RBI. One disturbing trend with Choo is that his slumps seem to be getting worse. Choo's .250 batting average through April could have been chalked up to simply a slow start but he followed by hitting .247 in May and through his first 13 games and has hit just .184 in June. Choo made headlines following his May 2 DUI arrest and since that incident is batting just .225/.312/304.

Daric Barton, A's

Worst slump of season: 8-for-64 (.125), April 16 to May 7.

Last season Barton proved that even without big slugging production from a traditional power position, a first baseman could still contribute with solid defense and good strike zone discipline. This season, however, Barton has fallen off the map. His .798 OPS last season is down to .591, a .207 drop. He's batted only .212/.327/.264, numbers that would have a utility infielder concerned. Never the prototypical first base slugger, Barton's Isolated Power (slugging minus average ) was only .144 and .131 in his two previous seasons but it's now down to a barely-visible .053. Barton seemed born from Oakland's Moneyball mold, walking 16 percent of the time in 2010 while striking out in only 18 percent of his plate appearances. Those numbers haven't altered dramatically in 2011 but Barton is a first baseman who has yet to hit a home run this season. In fact, Barton drove in only five runs in April and just eight in May. His Wins Above Replacement of 5.1 last season is now -0.4 this year, third-lowest among first basemen, ahead of only Lyle Overbay and Aubrey Huff.

Casey McGehee, Brewers

Worst slump of season: 6-for-52 (.115), May 21 to June 7.

McGehee has seen a .187 drop in his OPS from .801 last season to .614. In 2010, McGehee batted .285/.337/.464, but those numbers are down to .230/.287/.327. The production has vanished. From April 20 to June 15, McGehee hit only .218 with two home runs and 17 RBIs in 50 games. His BABIP: .330 in 2009 and .306 last year, is down to .257. Since his last home run on May 20 , McGehee has hit only .161 and slugged .169. McGehee is 28 years old and has played just two full major league seasons but this is a significant drop-off for a player whose 3.4 Wins Above Replacement last year is down to -0.3 this season. McGehee slugged .499 in 2009 and .464 in 2010, but this year's .327 slugging percentage ranks him ahead of only Miguel Tejada and Chone Figgins among third basemen.

Nick Swisher, Yankees

Worst slump of season: 9-for-54 (.167), April 7 to April 27.

Swisher's OPS has dropped as his profile has been raised. We see the Yankees' fun-loving outfielder in commercials, sitcoms and promos, but he's had a .142 OPS decline from .870 last season to .728. Swisher's .335 BABIP last season is down to .262. His batting average has dropped 59 points to .229 and his .511 slugging percentage from last season is at just .369. Swisher had one significant slump in each of the first two months of this season. He went without a home run during April's 9-for-54 skid and was then homerless again during a 5-for-34 slump in May. For the first two months of the season, Swisher batted just .213/.335/.314 with only three home runs in 49 games, but there is reason for optimism. Swisher has batted .293/.434/.610 in June with a 1.044 OPS. He has three homers and eight RBIs in 13 games this month. For the season, his line-drive percentage is at 20.6, his highest as a Yankee. Still, his career-high 4.2 WAR last season sits at just 1.0.

(Thanks to Dan Braunstein and Justin Havens of our "Baseball Tonight" research staff for their help with a portion of this post. Dan and Justin never slump.)

Follow Steve Berthiaume on Twitter: @SBerthiaumeESPN.