Roy Halladay is headed to the disabled list due to right shoulder inflammation, following seven brutal starts in which the two-time Cy Young Award winner surrendered nearly an earned run per inning pitched (8.65 ERA) and posted a walk rate (4.5 BB/9) approaching two and a half times his career average (1.9 BB/9).
Much has been made of Halladay's diminished velocity, as he has lost a tick off his fastball each of the past two seasons (91.5 MPH average in 2011, 90.5 MPH in 2012, 89.7 MPH in 2013). Hitters are taking advantage, slugging .574 against Halladay's not-so-hot heater this season after slugging about .390 in both 2011 and 2012. Halladay's slower fastball is getting crushed when batters swing. But there's another nasty side effect to his lost velocity -- opponents are swinging far less often when Halladay throws a fastball out of the strike zone.
Take a look at hitters' swing rate by pitch location against Halladay's fastball during his glory days in 2011, and during his hellish 2013. The pitch induced a healthy number of chases in 2011, especially on stuff thrown high. This year, he's not having any luck getting hitters to expand their zones against his sub-90 fastball:
Hitters' swing rate by pitch location vs. Halladay's fastball, 2011
Hitters' swing rate by pitch location vs. Halladay's fastball, 2013
Back in 2011, Halladay got hitters to chase his fastball 26% of the time. This year? Just 11%. That's less than half of the MLB average for starting pitchers (24%), and ranks dead last among all National League starters.
The difference between 92 MPH and 89 MPH might not seem career-altering at first blush, but it makes a difference to hitters. Since the start of the 2011 season, batters have chased 26% of fastballs thrown at 92 MPH, and have slugged .434. Against 89 MPH "heat," they have chased 24% and slugged .486. Halladay's decline in chases has been far more severe than most. But unless he comes back with his old zip, he shouldn't expect hitters to be as jumpy against his fastball as they used to be.