With only a few weeks to go until the All-Star Game and teams nearing the halfway point of their seasons, it’s as good of a time as any to review how some players at each position are doing in order to gauge their potential value in the second half. We’ll start this week at first base, with a few underachieving and potentially overachieving players that you can acquire or sell.

Carlos Pena was a fantasy monster in 2007, when he posted the third-highest VORP among first basemen-no small feat, considering he trailed only Albert Pujols and Prince Fielder in that category-by hitting .282/.411/.627, good for an EqA of .336. Those numbers were far and away career highs for the former prospect turned journeyman, but PECOTA wasn’t overly enthralled by his performance. His weighted mean forecast was a respectable .259/.372/.500, which makes him an attractive fantasy option, but far from a top-five player at the position. Even that expectation appears to have been too high, however. Pena has instead hit something closer to his 10th percentile forecast of .229/.335/.422. There are two things that stick out when trying to figure out what has caused Pena to hit so poorly, and those are his liner rate and his strikeout rate. For his career, Pena has hit line drives on 18.6 percent of his batted balls, but this season he’s only hit them on 14.5 percent of his balls in play. That is far and away a career low, below his previous low from 2004 with the Tigers, when he delivered a 16.5 percent rate while hitting .241/.338/.471 overall. Those “missing” liners have instead been fly balls, and Pena has not been able to drive them with any authority-he’s hitting homers on only 16.4 percent of his fly balls, a significant drop from 2007’s 29.1 mark.

As a matter of simple probability, Pena’s liner rate should recover somewhat, since 14 percent is well below what we can expect from major league hitters, but unless the Rays‘ slugger can get a handle on his strikeout rates we won’t see a huge boost to his numbers. He’s punching out in 34.3 percent of his plate appearances; combine that with his walk rate, and Pena is making contact just 53 percent of the time. It’s difficult to raise your batting average when you aren’t putting enough balls in play to do so. Now that he’s fractured an index finger, he’s hit a low point in value; if an owner has given up on him, it’s time to buy low, if only to watch his liner rate climb back up, though don’t expect to see flashes of 2007.

Kevin Youkilis is having the best season of his career this year, with a .300 EqA and .305/.376/.530 line that has him ranked fifth in VORP among first basemen. The odd thing about this is that Youkilis may be producing more by shedding part of a skill he’s known for: Youkilis has seen his P/PA drop from 4.3 to 3.9 this year, and he’s started to swing at more pitches outside of the strike zone (17.4 to 20.2 percent, via Fangraphs) while making more contact overall. Youk has lost some walks in the process-his unintentional walk rate has dropped from 12.3 percent of his PA to 9.2-but his strikeouts have remained around the same rate, giving Youkilis more chances to have a ball in play land for a hit. Youkilis’ patience oftentimes caused him to watch quality pitches he could have driven go by, but with the drop in P/PA and the uptick in his HR/FB from eight percent to 12, it may be that he’s jumping on those pitches and reaping the benefits of pitcher’s mistakes.

What worries me about Youkilis is that he typically wears down at the plate as the season progresses-he’s hit a combined .309/.410/.478 before the break from 2005-2007, and just .249/.355/.384 after that. That trend was still in effect in 2007 as well, when he managed just a .238/.356/.391 showing after the All-Star Game. It also doesn’t help that some of that added power has come from plenty of what Hit Tracker calls “Just Enough” homers. These are almost self-explanatory, homers that “cleared the fence by less than 10 vertical feet, or landed less than one fence-height past the fence.” Given this history, he’s the perfect sell-high candidate, especially when you can showcase the improvements he’s made at the plate to potential buyers without telling them about the short distance his homers have traveled or his second half struggles.

James Loney is hitting .296/.352/.440, good for a VORP of 11.1, which is only 15th in the majors among first basemen with at least 100 plate appearances. Considering the way he hit last season-.331/.381/.538 with an 11th-ranked 30.1 VORP in just 375 plate appearances last year-it’s easy to see why many owners have been disappointed by his production. Both of Loney’s part-time seasons in the majors have shown us a player with far more power than the one who’d been on display in the high minors-he slugged .546 in Triple-A in 2006, but with a .380 batting average, and had an ISO of just .103 at that level in 2007-but it seems as if this year his production has finally settled in around expectations created by his minor league career.

This isn’t to say that the 24-year old Loney is done growing as a player, and that at best he’s going to be a merely average first baseman. But today we’re only focusing on how Loney is going to do in the second half of 2008, a season where he is still experiencing the growing pains while holding an everyday major league job. For example, whereas last season Loney picked up hits in the middle of the outfield and distributed grounders in all directions in 2007, this season has seen him getting somewhat pull-happy, and grounding out consistently to the right side of the infield. He’s hitting .205 on balls hit to the right side of the infield, and those balls in play account for 36 percent of his total.

It also doesn’t help that Loney hasn’t hit a home run since May 21. Taken in total, Loney lacks the R, RBI, and batting average that you need from a first baseman who is also delivering little in the power categories, and with just a pair of stolen bases on the season (and just three for his career) you aren’t going to get anything on the side to increase his value to you. Loney still gets a lot of love for what he’s accomplished in the past, and he’s still just 24 years old, so the return you can get for him is probably worth more to you in 2008 than whatever he has left up his sleeve for the year.

Mark Teixeira has been disappointing in 2008, hitting just .269/.359/.437 in 309 plate appearances, placing him just above Loney, 14th in VORP among first basemen with 100 PA. There are a few items that may make holding on to him or buying low important to the fantasy owner in need of production at first base. First, Teixeira’s improved in a few categories that should have, in turn, improved his overall numbers. He’s swinging at a few more balls in the zone, and making four percent more contact on them than last year. By itself that doesn’t seem like a significant change, but when you add it to the drop in strikeouts-Teixeira is punching out in five percent fewer plate appearances than last year, and roughly three percent less than his career rate-you can see why it would make sense for Teixeira’s average to improve, not fall 37 points from last year’s total.

However, Teixeira has been unlucky on balls in play, with a BABIP of .294 despite delivering line drives on nearly 20 percent of batted balls. His BABIP should be around .320, which would bump his line up somewhat, but that doesn’t explain the drop in power he’s experienced this season. What keeps Teixeira from being a lock to reverse his fortune in the second half is his swing, which has lent itself to putting the ball on the ground in 2008. He’s hitting grounders 47.5 percent of the time, and that’s cut into his fly-ball rate that sits six percent below his career rate and eight percent under last year’s figure. Along with fewer fly balls has come fewer homers on fly balls; if it lasts the season, Teixeira’s 13.7 percent rate would be a career low for him.

If you buy low on Teixeira or hold onto him, you’re banking on the fact that either the Braves‘ coaching staff or Tex himself will figure out how to repair his swing. It’s mostly broken from the right side, where he’s hitting only .223/.330/.351 on the season. Given the Braves’ reputation for quality coaching as well as Teixeira’s positive indicators, a good second half does not seem out of the realm of possibility, especially when we consider Teixeira hit .305/.397/.585 after the All-Star break in 2005-2007. Either keep him or do your best to acquire him on the cheap during this low point in his career; you’ll be happy you did once he starts sending the ball into orbit again.