A.J. Burnett’s K/9 is at an uncharacteristically low 6.60 so far in 2010. That mark would be the lowest of his career since 2000, when he started 13 games (82.2 IP) for the Marlins in his second bit of action as a Major Leaguer (6.21 K/9). As a guy who was signed because of his strikeout abilities–career 8.28 K/9–this is pretty troubling. Let’s look at the ramifications of the lack of strikeouts before we get to any possible causes.
Because of the lack of strikeouts–and a fairly sharp increase in homers given up–A.J.’s FIP is all the way up to 4.96 (xFIP of 4.67). I thought that, perhaps, the lack of strikeouts would be reason for Burnett’s low strand rate (70.3), but it turns out that’s not really the case. That mark isn’t too far off of A.J.’s career percentage–71.9%–and there doesn’t seem to be any correlation between his strand rate and his K/9 in any given season. It appears that the only going up because of the lack of strikeouts–aside from the FIP–is his HR/9, but that link is rather tenuous. Let’s look at the batted ball data and see what that tells us.
Starting at the top, there’s A.J.’s BABIP. It’s at .308 this year, which isn’t all that high. His career mark is .295 so there isn’t much variance here. Burnett’s LD%, 16.8, is actually below his career rate of just over 18% so he’s not getting hit overly hard. Other than that, though, there isn’t a whole lot of change in his batted ball data. However, it’s worth noting that his HR/FB% is higher this year (12.5) than it has been for his career (10.4). So, when guys do hit balls in the air, they’re hitting it with authority.
So, let’s get to the crux of it: why is A.J. getting fewer strikeouts? I looked at Burnett’s Pitch F/X numbers to see what I could find there.
As you can see, he’s getting more swings and misses on his fastball this year, but the big difference is on the curveball. Last year, he got a swing and miss on number two nearly 17% of the time. This season, that’s down to 12.4%. As logic would follow, that curveball is being put into play more often in 2010 than it was in 2009. His curveball was worth 1.49 runs per 100 pitches last year. This year? -0.53. That pitch is Burnett’s punch out pitch and this year, it hasn’t been as effective as it should be or as Burnett wants it to be.
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One Response to A.J.'s K's
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TIQ IQ
Hi Matt, good stuff here.
My only comment/quibble is that if you’re going to compare the ’09 and ’10 Pitch F/X data to determine that his CB isn’t as effective as in the past, you have to at least mention that Pitch F/X seems to be saying that Burnett doesn’t throw the same repertoire in 2010 as he did in 2009.
2009: 64.3% four-seam fastball, 30.2% curveball, 5.5% everything else
2010: 47.3% four-seam fastball, 26% knuckle-curve, 24.9% sinker, 1.7% everything else
Now, I’ve always felt that Pitch F/X had a bit of a credibility issue but if we assume that their pitch classification info is correct here, then we can’t just blame the curveball for Burnett’s decrease in K/9. Based on what he’s throwing, he seems to be a different pitcher and it could be that the difference in curveball (CB in ’09, KC in ’10) is the culpable party here. It could also be that throwing a sinker (or throwing fewer of the four-seamers) is causing the breaking pitch to not “play up” as much as last year.
For the record, it’s also worth noting that the 2010 four-seamer is coming in 1 mph slower and has about 2 inches les armside run than the ’09 version of the same pitch. Since a curveball’s effectiveness is how it plays off a fastball, I’d imagine decreased velocity and movement — even with the development of a sinker — plays on how a curveball is treated by opposing hitters.