Originally written on Fangraphs  |  Last updated 8/2/12

Justin Upton is still a member of the Arizona Diamondbacks. During the off-season, there was no reason to think that the 24-year-old outfielder would be a potential trade candidate. Upton was coming off a phenomenal season, in which he hit .289/.369/.529, and finished fourth in the NL MVP voting. But things have changed in just a few months. While there seems to be some internal reasons for the team wanting to trade their star, Upton’s performance this season hasn’t helped matters. Upton has slumped to just .269/.358/.396. If Upton wants to dispel those rumors, he’s going to need to start producing like everyone expects. In order to do that, he’s going to have to start putting more balls in the air.

Upton’s career path has alternated between superstar-level production, and above-average player. In 2009 and 2011, Upton has looked like a superstar. In 2010 and 2012, he’s looked like an above average outfielder. Some of Upton’s struggles in those seasons can be attributed to his decreased power.

Year SLG WAR 2009 0.532 4.8 2010 0.442 3.0 2011 0.529 6.4 2012 0.396 3.2*

*Upton’s 3.2 WAR for 2012 is based on his rest of season ZiPS projection.

Power seems to be the key to Upton’s success. When he’s been able to hit home runs, he’s been an elite producer. And when we look at his batted ball data, particularly his pull numbers, an interesting trend emerges.

Year LD% GB% FB% 2009 15.3 61.8 22.9 2010 25.8 57.0 17.2 2011 14.8 52.5 32.8 2012 16.3 69.8 14.0

The chart shows Upton’s pull numbers over the last four seasons. In his two best seasons, Upton has been able to take advantage of his pull power. In 2010 and 2012, Upton’s FB% to left field has been under 20%. This season, he’s been even worse than usual, with just 14.0% of his pulled balls ending up in the air.

This is obviously also reflected in his home run numbers. More than half of Upton’s home runs in 2009 were pulled to left. It was even more extreme in 2011, when 22 of Upton’s 31 home runs were classified as pulled. In 2010, Upton pulled just seven home runs to left, which was the same number of home runs he hit to center that season. This season, Upton has hit just four pulled home runs. It’s also important to note that Upton has hit just one home run to center this season, which is also worrisome.

Upton’s power numbers haven’t just been affected by his pull numbers. Overall, Upton has beat the ball into the ground much more often this season. Upton’s ground ball rate has jumped to 45.2% this season, a far cry from his 40.8% career average. His fly ball rate has dropped even further, from a career rate of 40.0%, to 33.8%. While it’s easy to point to his career numbers and say that he’s bound to improve, that’s unlikely to happen this season.

Based on Pizza Cutter’s research, we know that it takes just 250 plate appearances for fly ball rate to stabilize. Upton has already reached 406 plate appearances, and there hasn’t been any significant change in his batted ball data that indicates he’s getting better after a slow start. Upton’s ground ball rate has actually gotten worse as the season has progressed. The last two months, it’s been above 50%. Unless Upton is able to show some significant changes in his final 250 plate appearances this season, his improvement is going to have to wait until next year.

It’s hard to know exactly why Upton has struggled to put the ball in the air this season. When he slumped in 2010, it was revealed that Upton had been dealing with a slightly torn labrum in his left shoulder. At the time, Upton was told to strengthen the shoulder. That seemed to work wonders last season, but it does remain somewhat of a concern this year. If Upton has re-aggravated his shoulder, that would definitely explain his struggles, and would likely lead to a more serious diagnosis this time around.

The shoulder is certainly a concern, but there’s been no talk of that type of injury this season. Upton did jam his thumb early this year. And while he wasn’t placed on the disabled list, he did have to have the thumb drained. It definitely possible that the injury is still a concern. Even if it’s fine now, it’s at least plausible to think that he adjusted his swing to accommodate for the injury, and that’s what has thrown him out of whack this year.

Upton has been a pretty big disappointment this season. His inability to loft the ball has really hurt his production. And while we don’t know the exact culprit behind his struggles, it seems unlikely that Upton will return to form this season.

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