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Perkins’ Improvements

The Twins have been a huge disappointment this year. For a team that’s been expected to contend in the American League Central every season during the past decade, Minnesota now is 15 games under .500 and in fourth place. But there’s one thing the Twins can take from this season — the emergence of southpaw Glen Perkins as a shutdown reliever.

A member of the Twins’ rotation in 2008 and 2009, the 28-year-old made the team out of spring training this season and took on a new role as a short-reliever. In the rotation, he was a low-walk, low-strikeout guy who allowed a few too many fly balls and homers (though his home run prevention improved in 2009). But in the bullpen this year, he looks like a completely different pitcher. His ERA/FIP/xFIP slash is 2.20/1.99/2.66, making him the only Twins’ pitcher to be below 3 in any of those metrics. And while Perkins’ K% (per plate appearance) sat around 11% during his 2008-2009 stints, it has skyrocketed to 27% this year — a number that Perkins hasn’t approached at any level since 2006 (between classes AA and AAA). His walk totals are still low, and his groundball rate — which has been on the rise throughout his career — is now at 51%.

Dipping into Perkins’ PITCHf/x data, we can look a little closer at what’s been different for him. The first chart shows Perkins’ pitch velocity (more about pitch selection later) on a game-average level since 2008:

After being in the low-90s in 2008, and dipping under 90 in 2009, Perkins’ fastball velocity has shot up since has been coming out of the bullpen. Now he’s been firing heaters in the mid-90s. Comparing his games in the bullpen against his games in the rotation, Perkins has shown a remarkable velocity difference:

|           | SI        | FF        | SL        | CH        | CU         |
| Starting  |     90.2  |     90.7  |     82.1  |     82.5  |     77.0   |
| Relieving |     92.7  |     93.7  |     83.1  |     83.1  |     N/A    |

Jeremy Greenhouse showed us in 2010 that pitchers typically jump 0.7 mph when going from the rotation into the bullpen. After averaging Perkins’ four-seam and two-seam fastballs together, you get a jump of 90.4 to 93.0, putting him in a league with fellow outliers such as Phil Hughes, Joba Chamberlain and Hong-Chih Kuo. As Greenhouse notes in his article, it’s unfair to pin velocity spikes solely on role; in Perkins’ case, for example, he’s returning from the arm injury he suffered in 2009 and might only now be getting his strength back. Whatever the reason, Perkins is throwing his fastball at a velocity he wasn’t approaching a few years ago.

His pitch selection has changed, as well. Perkins has primarily thrown a two-seam (sinker), a four-seam and a slider this year after tossing plenty of curves and changeups when he was in the rotation. He threw a curveball early in he career but ditched it for a harder slider in July 2008. Since then, he’s only thrown two curves (if that many — they might be slow sliders). His changeup usage also has diminished — he’s thrown only 13 this season. Rate-wise, he’s down from a bit under 20% against right-handed batters in both 2008 and 2009 to just 3% this year.

So what’s behind the surge this season? A simple answer that satisfies this question is that his strikeouts rates per pitch have gone up considerably since 2008. Look at the graph, but be mindful of the small sample size in 2010:

Approximate league-average whiff rates for these pitch types are 12% for sinkers, 16% for four-seamers, 28% for curveballs, 30% for changeups and 31% for sliders (courtesy of Harry Pavlidis’s benchmarks).

Perkins was basically below average at everything as a starter, but this year his four-seamer and slider have become well above average. Keep in mind, though, that Perkins usually throws sinking fastballs (which elicit more contact than his four-seamers) to generate ground balls. You could assume that the jump in four-seam strikeout rate is mostly due to the extra velocity, but the slider is tougher to put a finger on. The velocity is up a bit, but not as much as the fastball. Still, two things are in his favor: the slider is getting one and a half inches more in vertical break and is (on average) located two and a half inches lower in the zone this year than in previous seasons. I would guess that these factors play a role in the strikeout-rate increase.

It’s expected that starters get better results when pitching out of the bullpen, and Perkins has clearly benefited from his move. And during a down year, Twins’ managements needs all the bright spots they can find.