Where Is Buster Posey?

The San Francisco Giants and Brian Sabean are quickly running out of excuses to keep former fifth overall pick Buster Posey off their 25-man roster. Improbably, the Giants are 22-21 and right in the thick of the NL West race, only 3.5 games behind the Padres. Buster Posey is 23 and has a .960 OPS at AAA after putting up a .902 OPS at the same level in 2009. Meanwhile, the Giants offense has a wOBA of .316, sitting 14 runs below the league average.

The strong performance of Eli Whiteside has been a decent enough reason to keep Posey in AAA so far. His .383 wOBA currently leads the Giants, but that’s completely unsustainable given his paltry walk rate of 3.8%, a BABIP of .364, and a HR/FB of 14.9% that suggests above average power when he has hit only 15 home runs in the minor leagues in just over 500 PAs since 2007. Even considering his solid start, ZiPS only projects Whiteside to post a .296 wOBA the rest of the season.

Perhaps starter Bengie Molina’s roughly league average performance (.332 wOBA) is keeping Posey off the roster? Molina is posting a career high walk rate of 8%, but his power has all but disappeared. His ISO is down from .177 to .084, and as a 35 year old catcher, Molina is certainly at the age where a drop in HR/FB rate could just as easily be decline as random variation. Even if Molina continues to produce at this clip, his hitting is his only asset. Last season, Bengie Molina was 4.5 runs below average on the bases according to Baseball Prospectus’s EQBRR. According to our own Matt Klaasen’s catcher defense rankings, Molina has already been 3 runs below average, and was another 3.4 runs below average last season.

Supposedly, defense is the reason that the Giants are keeping Posey down in the minor leagues. Posey has excelled with the arm this year; he’s thrown out 44% of basestealers so far this season. That reason, however, breaks down when we see Buster Posey spending time at first base as he is in today’s lineup for the Fresno Grizzlies.

Posey’s MLE for his current line at AAA is a .293/.366/.437 triple slash line. Prior to the season, both CHONE and ZiPS projected Posey as a roughly average major league hitter, just above what they projected Bengie Molina. Taking into account defense, baserunning, and upside, and Posey was surely the correct choice for a team wanting to make a run at the postseason. Posey is producing at an even higher level in AAA this season, suggesting that he’s even better than these pre-season projections.

Especially with the position that the Giants are in right now, there is no excuse for Posey to remain in AAA. He has nothing left to learn there. The Giants need has bat in the lineup, and they need it before they lose any more ground to San Diego and Los Angeles.