We’re nearing the halfway mark in the season, and as teams begin to ponder whether they’ll be buying or selling, and weigh their status as contenders or acknowledged pretenders, a look at the other side of the equation is in order: identifying problem positions that teams will need to address because of the drag those positions have placed on a team’s performance.

Using the Value Over Replacement Player measurement, who are the worst contributors to their team’s lineups, and can or should something be done about them? In some cases, it’s a matter of a slow start, which makes it possible that a player might bounce back. There are also the prospects that might not be performing, and/or they are prospects saddled with playing for non-contenders, making it easy to understand why their teams are playing them regardless of their performance. Other players, however, have been begging to be replaced for a couple of seasons, and are performing so badly that they could keep their teams out of postseason money. In those cases, something must be done.

It’s no surprise that you’ll find a prospect with upside who is playing because he’s there to take his lumps, and, with any luck, become a building block toward improving the future of his hapless team. In this category, you’ll find the Royals’ third baseman and former favorite for the Rookie of the Year award, Alex Gordon (-6.5 VORP), as well as Tampa Bay D -Rays catcher Dioner Navarro (-10.4), and rookie slugger Adam Lind of the Toronto Blue Jays (-4.5). The three players have been awful, but their teams don’t really have great alternatives, and their individual success or failure is perhaps even more important than where the teams finish in the standings. The Arizona Diamondbacks right fielder, Carlos Quentin, is an interesting contrast. Quentin showed much promise when he made his debut last season, but he has gotten off to a slow start for the contending Snakes (-4.6 VORP). The risk is that if he doesn’t heat up, he could lose playing time to Scott Hairston or Mark Reynolds, but Arizona might also decide to up the stakes in the NL West by trading for a bat.

Quentin’s struggles reflect the difficulties in deciding what to do with slow starters. Looking at the list of the worst regulars, Omar Vizquel and Corey Patterson have been awful, but do their teams have much in the way of alternatives? Finding a readily available replacement that represents an offensive upgrade is never easy at important defensive positions such as shortsop or center field. The Giants don’t have a shortstop handy to replace their future Hall of Famer, Vizquel, and roving multi-position infielder Rich Aurilia probably couldn’t handle the demands of playing short every day even if they asked. Moreover, it isn’t as if Aurilia’s performance has been especially valuable, considering that he’s hitting .241 AVG/.284 OBA/.353 SLG. Patterson’s renaissance with the Orioles last season was among Baltimore’s few highlights, so it’s not surprising the team would stick with him. The problem is that his collapse reflects a continuation of the club’s longstanding outfield woes.

For the White Sox, losing Joe Crede to a back injury perhaps gives them an easy out from his slow start, since they can take a time-out from the popular veteran and onetime postseason hero to consider a top prospect, Josh Fields (.283/.394/.498 at Triple-A Charlotte before his promotion to the majors last week). Houston’s Craig Biggio is in a special category of his own among veterans you maybe wish would just go away. The future Hall of Famer is flailing his way toward his 3,000th career hit (16 to go and counting), but his offensive production has been so weak (.227/.272/.382, with the 16th-worst VORP in baseball at – 5.0) that he’s partially responsible for the Astros’ failure to contend in the always-weak NL Central.

Which brings us to the worst, the guys who are bad and playing on teams that have something at stake. The worst of the lot has been Jason Kendall, who’s so done he’s like the Thanksgiving turkey in which the meat thermometer has been melted to plastic slag. The former Pirates star has seen his performance flag ever since coming over to the stronger junior circuit, but whereas in his first two seasons in Oakland he posted OBPs useful enough to allow his team to overlook his prodigious ability to ground into twin killings (49 GIDPs in 2005–06), this year his production at the plate has cost the A’s a full win in the standings relative to replacing him with a replacement-level catcher — not a good catcher, and not even a merely average catcher. Oakland’s recent call-up of prospect Kurt Suzuki might give A’s fans some hope that this — the last year of Kendall’s deal — will be his last with the team. Suzuki’s production at Sacramento (.280/.351/.365) was less indicative of prospectdom than was the importance of not being Jason Kendall. Still, it remains to be seen if A’s manager Bob Geren will start moving Kendall out of the lineup.

Conversely, the division rival Angels have their own fixable sinkhole at DH, where veteran bopper Shea Hillenbrand looks as if he’s at the end of the road as well. The Angels already seemed to be phasing him out of their lineup with Garret Anderson back off the DL, but if they’re smart, they’ll be thinking about adding a bat that lets them put the ‘H’ back in DH. Similarly, the Braves have probably taken the experiment in which they replaced Adam LaRoche with Scott Thorman about as far as it can go. The team needs to get a first baseman who can hit if they want to catch the Mets and win the NL East. Finally, the Cardinals aren’t so far out of it that they couldn’t make an even more difficult decision with Adam Kennedy at second. However much it might hurt that they spent $10 million on him this past winter, with two more years to go on his contract — if he’s losing playing time to utilityman Aaron Miles, you know that Cards general manager Walt Jocketty recognizes he has a problem.

Ms. Kahrl is a writer for Baseball Prospectus. For more state-of-the-art commentary, visit baseballprospectus.com.