With just September ahead on the schedule, it's time to look at who has wilted in the heat of the summer. With an eye towards both the remainder of this year and 2011, let's take a look at some of the worst performances of the second half via to see what we can learn.

Brennan Boesch was due for a regression, but the 25 year old rookie has scuffled even more than expected the past two months. Prior to the All-Star break, Boesch was hitting .342/.397/.593, but since then he's put up a paltry line of .152/.218/.225—in 92 fewer at-bats, he has 10 fewer homers, never mind the nearly 200 point drop in batting average.

Boesch has a line of .269/.329/.452 on the season, which isn't terrible, but it has been falling. His .278 TAv puts him a few points below the positional average for right field (.283) but if he continues to post such horrid numbers we'll see that gap widen in the last month of the season.

Boesch has an odd split—the left-hander has performed worse against righties (.244/.301/.411, 299 at-bats) than southpaws (.347/.406/.579, 95 at-bats). Reverse platoon splits do occur, but we'll chalk this up to sample size for now, and take his performance against right-handers to be a sign of his true production level at this point in his career. Boesch has also performed worse on the road than at home, which is odd given he plays in a pitcher's park—I'm less concerned about that split, as the most basic thing to take from it is that he has been lucky at home and unlucky on the road. It's tough to tell from such a limited amount of data though.

Boesch is young and could improve, but he is still the player he was when the year began: a player with gigantic holes in his swing. As pitchers saw more of him, they learned to exploit him, and unless he adjusts to that exploitation, you can expect a lot more of the second half than the first half out of the outfielder going forward.

Denard Span had a very promising start to the year, despite a lack of power production. He had 16 steals against one caught stealing prior to the All-Star break, which was a huge improvement for him over his 2009 season when he swiped 23 bags but was nabbed 10 times. His ISO in the first half was .102, close to 2009's .104 mark despite the presence of the pitcher-friendly Target Field. The second half has not been as kind to him though, as Span has stolen just three bases while being caught three times, and he has been picked off a grand total of eight times as well. He has also hit just .261/.311/.303 since the All-Star break, which has dragged his line down considerably.

Span was a player I pushed this spring because I believed we would see more and better running from him on the basepaths—it looked like I knew what I was talking about when he was 16/17 to start the year, but the pickoffs and slowed running in the second half have dulled the sharpness of that thought. This could just be a minor problem though, as there is more of a record of him being an effective base stealer than what he has been the past few months, but it is something to keep in mind (and watch out for this September) if you were planning on keeping Span around for 2011.

Ben Zobrist has had a disappointing season in the sense that he hasn't been a fantasy monster, but he's still managed to be productive for the Rays. His .278 TAv is close to the right field average, and though it doesn't matter so much in fantasy baseball, his defense makes him an above-average player when combined with that bat. He was looking better prior to the second half though, as Zorilla has hit just .167/.288/.238 since the All-Star break.

It's tough to pinpoint the problem—he's not hitting lefties or righties particularly well, and his home/road splits show the same kind of shared disappointment. He's hit poorly on turf this year relative to grass, which was not the case in previous years—from 2007-2009, Zobrist hit .281/.394/.525 on turf and .256/.332/.459 on grass, while this year he's at .235/.365/.317 on turf and .267/.349/.387 on grass.

His infield hit percentage is up though, so those numbers don't mean as much as they look like they do. In addition, it doesn't matter what surface you play on when the ball ends up in the bleachers, and that just hasn't happened for Zobrist in 2010 despite two strong seasons of power beforehand. Zobrist is popping up more than he had the past two seasons though—his 11.6 percent pop up rate is along the lines of what he put up in limited duty with Tampa Bay in 2006-2007, when he didn't look like much of a hitter. He's still hitting as many flyballs as he was, but between a drop in liners and an increase in the number of harmless pop ups he's hit, it's no wonder his production has fallen so far.

The most likely culprit is his swing—if he's popping up on nearly 12 percent of balls in the air, he's not generating the proper combination of drive and loft in his swing. You can see the difference in distance on his balls in play with these charts from Texas Leaguers:


In 2009 Zobrist put plenty over the fence, but he also hit a considerable number of long fly balls to go along with the singles, doubles and triples that fell short of the warning track. As for 2010:


The ball just isn't carrying as far off of his bat in 2010—he has nowhere near as many deep fly outs, and the number of homers has dwindled considerably as well. The average distance of his homers according to Hit Tracker is 377.9 feet and at 100 miles per hour off of the bat, whereas in 2009 he was at 384.4 and 102 mph off of the bat. That may not seem like much, but slashing 6.5 feet off of every flyball can have adverse affects (and this is just the distance change in the ones he got a hold of).

His swing was corrected once, and the result was an 826 plate appearance stretch where he hit .285/.387/.532 with 39 homers and 86 extra-base hits in all. If he can get back to driving the ball, we'll see a different Zobrist then what we have in 2010. Keep an eye on his September to see if he can shake his current slump and regain some of his past glory.

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Zobrist is hurt. He missed some time with back pain. It's quite possible he's had some back pain all season, and it's sapping his strength.