Wednesday, May 7, 2014

A star lefty, in decline

Over the last three years, including thus far in the 2014 season, this highly touted ace has seen his ERA rise almost a full earned run between both 2012 and 2013, and 2013 and 2014, and is now solidly below average. He's been victimized by a decline in ground balls (53% in 2012 to 42.6 in 2014) and a lot more fly balls leaving the park (15.7% in 2014, compared to a 9.4% on his career).

Fastball velocity, 2012 - 2014
Why the big declines? Fastball velocity is the likely culprit, as his average fastball is 3.3 miles per hour slower than it was in 2012, and is lower than it was in 2013 as well. The odd part of this story is that his peripherals are actually better than his career norms - he's striking out more batters than he ever has in his career (10.17 K/9, compared to 8.20 on his career), and has the lowest walk rate of his career, a microscopic 0.92 BB/9. To top it all off, his swinging strike rate is elite (11%), and is easily the best of his career.

It might surprise you, but this lefty isn't, in fact, CC Sabathia, but rather Tampa Bay Rays ace David Price. They have experienced similar declines, though. Price experienced a big decline in fastball velocity in 2013, but it was overshadowed by his spectacular second half. Now, in 2014, he's lost even more velocity and the home runs are piling up.

Sabathia, as has been well noted in many places, has experienced a similar perplexing decline. Despite his career best strike out rate and near career best walk rates, Sabathia's ERA is a bloated 5.75. Unlike Price, CC is also inducing more groundballs than ever, but if a ball is in the air, it is leaving the park at an alarming rate (21.9%, compared to a career rate of 9.3%) and a rate that is 50% higher than the leader last year among qualified pitchers (Joe Saunders at 14.5%).

All in all, it is a rather confusing picture for both pitchers, and it really presents an interesting look at how the underlying statistics can tell us conflicting stories of player performance. At the most basic level, we can see that Sabathia and Price's ERAs have risen substantially, despite the fact that their strikeout and walk rates indicate that their ERAs should be elite. For both pitchers, their swinging strike rate and first pitch strike rates, which are excellent predictors of strikeout rate and walk rate, support these numbers. Often times, people point to a sky high home run per fly ball rate as just bad luck - it tends to normalize around 10%. However, the decline in velocity is often associated rising home run rates, so it probably isn't reasonable to expect these two pitchers to end up at 10%, when all is said and done.

Are David Price and CC Sabathia pitching better than their ERAs (4.44 and 5.75, respectively)? Probably.

Are David Price and CC Sabathia pitching as good as their peripherals (2.56 and 2.91 xFIP, based on strikeout, walk, and ground ball rates)? Probably not.

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