Four Factors: Kemp’s Down Year

Barring one of the most unlikely 60 plate-appearance-runs in baseball history, Matt Kemp’s 2010 season is bound to go down as his worst full season as a Major Leaguer. After putting up wRC+’s above 115 and wOBAs above .349 from 2007-2009, Kemp has a .314 wOBA and a 97 wRC+ in 618 plate appearances this season, which is about 25 runs worse on offense than last year. As Kemp has served as one of the Dodgers’ franchise players, the drop in performance has to be particularly worrisome for those in the LA front office.

Diving slightly beneath the surface, we can see that the culprits aren’t exactly his power stroke nor his ability to reach via the walk. Kemp’s 7.9% walk rate is nearly a percentage point better than his career average and his .181 ISO is exactly in line with his career mark. That leaves the other two factors of hitting – strikeout rate and BABIP – as culprits for this decline. Indeed, Kemp has seen has BABIP fall down to earth, a league average .299 mark after posting .340 BABIPs or better from 2007-2009, and his strikeout rate has skyrocketed from 22% to 28%.

Just over half of this decline can be attributed to Kemp’s relative BABIP issues. The nearly 40 point drop in BABIP has cost Kemp nearly 30 points in wOBA according to the Four Factors method. That leaves the other twenty points remaining between his .314 wOBA and his typical .360-.370 wOBA to his strikeout rate, which is confirmed by the method.

The difference doesn’t really get us much closer to understanding why Kemp’s numbers are down, we just know with which components of the game he’s struggling. Part of it is probably luck and random variation, but I believe a more significant cause can be seen in Kemp’s plate discipline numbers. Kemp thrives on making excellent contact, as that spurs not only his power production but also his excellent prior numbers on balls in play.

The best way to make solid contact is by swinging at pitches that are the easiest to hit – ostensibly, those that fall inside the strike zone. Kemp has had issues with that this season, as his Z-Swing% has fallen from 72.5% in 2008 and 68% in 2009 to 64.5% in 2010. Meanwhile, he’s still swinging at over 30% of pitches outside of the zone – it’s not simply a matter of Kemp swinging less. Combine this lack of swings at pitches in the zone with a lack of contact on pitches in the zone – a Z-Contact rate down by five percentage points this season – and Kemp is putting roughly the same amount of pitches in play, but fewer of them are of the easier kind to hit- the inside the strike zone variety.

It’s possible I’m missing something here – say, a hitch in Kemp’s swing – that I would have had to see more than a select few of Kemp’s plate appearances this season to adequately judge. But the numbers definitely suggest that Kemp’s struggles are due to striking out more and reaching on fewer balls in play – that’s hard to argue. Kemp’s plate discipline numbers suggest that he’s not hitting the more hittable pitches he’s seeing this year, which is making it difficult for him to maintain the brilliant BABIPs that have sustained his hitting lines to date. Regardless whether this is the case, Kemp and the Dodgers need to figure the reason why quickly, because Kemp is simply not a productive player if his bat continues to play at this level.