Tuesday, April 21, 2009
If you're a Twins fan, and I'm going to assume you are, you've probably noticed that Glen Perkins is by far the best starting pitcher on the Twins this season. I couldn't help but wonder, "Why?"
This season, Perkins is sporting an ERA of 1.50 and a WHIP of 0.83 in his three starts, lasting through eight innings each time out. Last season, his first full and first time as a starter, Perkins had a nice shiny record at 12-4, with a less impressive ERA of 4.41 and a WHIP of 1.47 - ok, but slightly worse than league average in both cases. So is this a case of a young pitcher figuring things out, or simply a hot start? Since the three games were against the Angles, Blue Jays, and Mariners (only one of which has been a quality offensive team this season) it warrants some research.
We have this article from the AP, full of nice fluffiness and rainbows and cuddles, letting us know that "this spring his attention to detail, be it fielding his position, doing squats in the weight room or studying the opposition, has been keen", comparing him to Johan Santana (seriously), and that his dad thinks "It’s just gratifying as a parent to see that [maturity] in your children." Ok great. It's an article full of quotes and interviews and pats on the back, but very little substance and quantitative analysis. So let's go to the Nerd-Stats-Mobile, thanks to FanGraphs.com.
The first thing I always check when evaluating if a player is improving/regressing compared to simple luck is Batting-Average-on-Balls-In-Play (BABIP), or simply, what usually happens when the ball is hit. Generally, the league average is right around .300, and most pitchers will be within twenty or so points of that. Anything outside of that variance starts to look a little bit more like luck, good or bad. Last season, Perkins came in with a BABIP of .310, a number right about where you would expect. This season, his is sitting at .223, a ridiculously low number. Hmmm. This bares further analysis, but at first glance, I would say we shouldn't expect him to keep up at this pace. How far he regresses to the mean is to be determined.
Next up, let's figure out what exactly is going on when the ball is put in play. Again, according to FanGraphs:
Line drive percentage is, well, the percentage of balls put in play that are line drives, and as you could guess has a pretty solid correlation to hits allowed. Perkins having lowered his from 22% last year to 15% this year is a tremendous step, and gives some insight into why he's having this kind of success. Also of note is that although his fly ball percentage has increased (from 40 to 46%), generally a bad sign, but it's tempered by the fact that his infield fly ball % went from 8.5 to 18%, which is excellent, as obviously infield pop-ups are not very scary. The 18% is probably not sustainable (Garza led at 18.1% in 08, Bronson Arroyo at 15% in 07), but if he can keep the number in the teens it bodes very well for future success.
With these numbers, along with strikeout and walk rates that haven't changed much, I would tend to say that he would be improved over last year, but thus far would lean more towards mirage than trend. However, there is one big factor that I think lends more hope to a breakout season, and that's Perkins change in approach.
Here are his percentages of pitches thrown the last two years:
Last season, Perkins threw his fastball 70% of the time and his changeup 15%, and this remains relatively unchanged this year. The big difference is that he has abandoned his curveball, and has come to rely on his slider quite a bit, throwing it 17% this year compared to 7% last year, with the curve going from 7% to 0%.
The results have been staggering. Last year, Perkins induced opponents to swing at 23.7% of his pitches outside the strike zone, one of the worst numbers in the league. This season, he's improved that to a whopping 38.2%, with opponents making contact with those pitches 76% of the time. This means that 29% of the time he throws a pitch outside the strike zone, the batter is putting a bad pitch in play - this goes a long way towards explaining the improvements in his other metrics. That 38% is second in the majors this year to Jamie Moyer, another crafty left-hander.
I wish there was a way to see pitch-by-pitch data, such as what % of the balls swung at outside the zone are sliders and if his curve got hit around a ton last year, but I can't find that data anywhere. I could have sworn it existed, and if you're reading this and know of it please let me know.
As it is, this is what we have. I find it encouraging, but certainly not conclusive. Can Perkins keep up a 1.50 ERA and a WHIP of 0.88? No, of course not. Could you actually become the team's ace? I think he has a shot. If he can get batters to keep chasing his slider and keep getting them to hit his pitches and hit them weakly, he can have a ton of success. His low strikeout total doesn't generally indicate a possible staff ace type, but it's been done before. Tom Glavine struck out a similar amount of batters throughout his career, and he's heading for the hall. Doug Drabek and Bob Welch both won Cy Youngs with a similar number, so it is possible to put up an elite season without striking people out.
Final Verdict: Closer to a trend, but with some caveats. Don't expect him to crack the top five in the Cy Young voting, and I'd say there's a small chance he implodes if teams start laying off the slider, but I'd look for a very, very nice season from Mr. Perkins the rest of the way.
Of course, you know what this means.......