Tuesday, April 12, 2011
Velocity, strikeouts, and Colby Lewis’ rough startPosted by Derek Carty at 10:00am
|Colby Lewis is off to a rough start in 2011. Should his fantasy owners be worried? (Icon/SMI)|
I drafted Lewis on three of my teams this year (Tout Wars, Cardrunners, and Yahoo! Friends & Family), in addition to two teams last year. I also made a bet with Eric Kesselman (co-commissioner of the Cardrunners expert league) that Lewis would be worth at least $18.5 in a 12-team, AL-only format this season. Needless to say, I was pretty high on Lewis coming into the year.
Through two starts this season, however, his fastball velocity is down. Andrew pointed out a Mike Podhorzer article at FanGraphs that listed the pitchers who have suffered a decrease in velocity to start 2011. Lewis' average velocity is 87.9 mph this season, down 2.2 mph from 2010. That's not something to be taken lightly.
The radar gun and sample size
Some concerns were raised in the comments of Mike's post about the accuracy of the radar guns this year, and although the stadiums Lewis has pitched in weren't mentioned, that's always a possibility. It also should be noted that the velocity readings Mike noted are from Baseball Info Solutions. The PITCHf/x guns are a little more favorable for Lewis, who loses only 1.7 mph based on them.
Furthermore, Lewis hasn't used his fastball as much this year, and therefore has only thrown a total of about 70 (according to PITCHf/x) or about 90 (according to BIS). When you consider that he threw over 1,800 last year, we're not looking at very many.
Velocity's impact on strikeouts
Before going any further, we must first figure out how important velocity is for striking out batters. Dave Cameron ran a study at FanGraphs a couple of years back that looked at the correlation between a pitcher's fastball velocity and his strikeouts per nine innings. I've basically done the same thing here and reached similar conclusions. Looking at all pitchers since 2002 with at least 125 innings pitched, I found a 0.21 r-squared, which means that fastball velocity explains 21 percent of the variation in a pitcher's K/9.
This is highly significant, but not damning for a pitcher. This means that nearly 80 percent of a pitcher's strikeout rate comes from something other than his velocity. (Caveat: the pitcher may not necessarily control all 80 percent.)
Application to Lewis
That's very good news, but we get even better news when we look at the regression equation derived from the above study. If we apply it to Lewis' 2010 stats, based solely on fastball velocity, we'd expect Lewis to post a K/9 of 6.5. That's much lower than his actual figure of 8.8*. Based on Lewis's decreased 2011 velocity, his expected K/9 would be 6.0.
This can be seen as a positive thing for two reasons:
- Lewis' "expected" K/9 was much lower than his actual K/9 last year despite him likely deserving his actual K/9. This likely means that Lewis is able to do things other than merely having a fast fastball to strike batters out. It's possible that a pitcher like this can lose a tick off his fastball and still be successful.
- Lewis' "expected" K/9 dropped only half a point anyway. That's hardly going to destroy his numbers.
*You could argue that it's one year and Lewis didn't deserve the 8.8 K/9 last year, but I'd argue against you based on his stuff and his terrific MLEs in Japan the two seasons before. THT's Oliver system projected an 8.4 K/9 for Lewis this season, and ZiPS is even more bullish at 9.0.
Historical velocity dips
I decided to run one more study to examine other pitchers who lost some velocity in April and see how often their velocity returned over the rest of the season. Using PITCHf/x, I looked at all pitchers since 2007 (the year it was introduced) who had lost at least 1.5 mph off their four-seam fastball between the previous season and April. I then looked at their velocity for May through October and compared the three.
To qualify, a pitcher needed to throw at least 1,000 fastballs in the previous season, 100 in April, and 600 in May through October, which gives us a sample of 23 pitchers.
+---------+-----------+---------+ | Y-1 MPH | APRIL MPH | M-O MPH | +---------+-----------+---------+ | 91.2 | 89.3 | 90.2 | +---------+-----------+---------+
While our sample size is less than ideal, this tells us that, on average, pitchers who lost at least 1.5 mph on their fastballs in April regained 52 percent of their velocity over the rest of the season.
For Lewis, that would mean that his fastball velocity would rise to 89.2, an overall drop of just 0.8 mph from 2010. If we plug this into our "expected K/9" equation, Lewis's expected K/9 would be 6.3 with an 89.2 MPH fastball. That equates to just a three percent drop in strikeouts for Lewis based on his velocity loss.
If we look at the results a slightly different way, we see that 87 percent of the pitchers in our study improve their April fastball velocities in the following months. Just four percent end up reaching their previous velocity level, but 22 percent get within 0.5 mph.
Prognosis for Lewis
Summing everything up, things don't look terrible for Lewis. He has a few things going for him:
- The PITCHf/x gun sees only a 1.7 mph drop on his fastball.
- Lewis has thrown a relatively small sample of fastballs so far this year.
- Lewis uses a lot more than his fastball velocity to strike batters out.
- Since 2007, pitchers in this situation end up regaining 52 percent of their lost velocity.
- For Lewis, regaining 52 percent of his lost velocity would result in just a three percent total reduction in strikeouts the rest of the way.
- Even if Lewis doesn't regain any of his velocity, his expected K/9 would still drop by only half a point.
Maybe I'm trying to put a positive spin on things because I have such a vested interest in Lewis' success this year, but I don't think it's time to hit the panic button yet. We're just two starts into the season, and a lot can still happen. If a Lewis owner is panicking, it might be wise to acquire Lewis cheaply. If you're the Lewis owner, I don't think we have much of a choice but to wait and see what happens. I have a feeling we'll be fine, though.
Derek Carty, 23, has also been published by NBC's Rotoworld, Sports Illustrated, FOX Sports, and USA Today. This season, he'll be contributing to FanDuel and will be linking to all of his work at DerekCarty.com. In his three years competing in expert leagues, he has won 2 titles with 4 top three finishes, including a LABR NL title in 2009, making him the youngest person to ever win a major expert league title. Derek is a proud graduate of the MLB Scouting Bureau's Scout Development Program and is a firm believer in the importance of combining stats and scouting. He welcomes questions via e-mail, Facebook, or Twitter.