The Continuing Rise in Strikeout Rate
In yesterday’s post on the early home run trend of 2013, I noted that strikeout rate was up again, as it has been for a while. At this point, the continuing rise of strikeout rate isn’t a new story, and I think most of you are probably aware of the fact that Major League Baseball is essentially setting a new record high for league average K% each season.
One of the main theories that is espoused for why strikeout rate is ever increasing is the simultaneous increase in pitcher velocity. It used to be that Randy Johnson was a freak because he could touch 100 mph with his fastball, but now it seems like every team in baseball has a guy who can hit that mark. While we don’t have historical velocity data, we do have PITCHf/x velocity data since 2007, and BIS velocity data going back to 2002. While there are some differences due to the classifications of pitch types, both support the idea of rising velocity.
The BIS data has the average fastball going from 89.9 in 2002 to a peak of 91.6 last year, a nearly 2 mph rise in the average fastball speed over the last 11 years. We know that velocity and strikeout rate are highly correlated, so a league wide rise in the speed of pitches would explain why strikeout rate keeps going up and up.
