Much speculation has been given to the Rays trading for Justin Upton this offseason. In 2011, Justin Upton was a beast with a .592 slugging percentage and .240 ISO during his 6.4 WAR campaign. In 2012, Upton saw a shift in his hit distribution and a significant decrease in his power production that have led many to label him a disappointment.
So what's wrong with Justin Upton?
Upton has found most of his success by pulling the ball down the left field line, but lost that ability in 2012.
If we look at his career pull numbers, we can glimpse into Upton's development. These are his pull percentages over the last four years:
In 2010, Upton was laying the ball too low and had a high LD% - most commonly attributed to a slight tear in his left labrum - but by 2011, Upton had strengthened his shoulder and worked a high FB% to left field. 2009 was the mark of Upton's rise in power, hitting 15 of his 21 homeruns to left, and Upton repeated this trend in 2011 with 22 of his 31 longballs getting pulled.
Last season, the pull-trend dramatically regressed to center field, and someone pulled the plug on his power. The shift could be due to an aggravated shoulder, but during the injury in 2010, Upton produced an uptick in line drives while maintaining a decrease in ground balls. 2012 saw the opposite.
The process by opposing pitchers saw a significant change in regards to off-speed pitches during 2012. Upton made pitchers pay on slow stuff in 2011. He didn't see much less of those pitches in 2012, but they were mostly out of the strikezone and away, and Upton generally avoided swinging at them, making it a moot point.
You would think that Upton would have seen more fastballs in response, but the frequency and distribution of hard stuff saw only minor shifts in 2012. Pitchers were throwing Fastballs, Cutters and Sliders slightly less often, and with a subtle shift from the outer third of the strikezone to the inner third.
So if there was little change in fastball distribution, what was he doing with the hard stuff?
2011 ISO on Hard stuff:
2012 ISO on Hard stuff:
The difference appears to be in Upton's swing, and it is here that my knowledge on baseball reaches a breaking point, and I offer you the same question. What happened? Could it be Upton's shoulder again, or is it his approach?
Looking into his RHP vs. LHP splits, Upton did have a few issues against southpaws in 2012. His percentage of swings on pitches near the middle of the plate fell around 10%, and on pitches high and low outside he took more swings in 2012 than in 2011. Perhaps this is the culprit behind his increased GB%, but this does not seem to be a comprehensive answer.
The Good News
By the numbers, it would appear that Upton began making his adjustment back to his previous swing in July. Much like his adjustment between 2010 and 2011, there was an uptick in LD% before Upton found his flyball again.
Is it safe to believe the 2011 Upton could return?
Justin Upton did have an injury in early 2012, jamming his left thumb on April 10 while sliding into second base. Upton was listed as Day-to-Day, eventually having an MRI a week later and draining some fluid from the joint. The injury was aggravated on April 22 on a hit-by-pitch and likely contributed to his offensive struggles.