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Through his five April starts, Patrick Corbin was pitching very well. He had a 2.25 ERA and was 4-0. The velocity on his fastball was sitting at the same place where it had spent the vast majority of the 2017 campaign. But as the calendar page changed to May, Corbin changed too. In April, his average fastball per outing ranged from 92.4 to 93.5 mph. But this month, the range has been 89.7 to 90.9 mph, about 2.5 mph less than in April. The team and Corbin have both said there’s no physical ailment involved, but have been taking steps to see if they can re-find the lost velocity, such as skipping bullpen starts. However, the two starts since that piece was written have shown little if any change.
On the surface, the numbers by Corbin have still been very good: a 2.76 ERA in May hardly seems like cause for major concern. But the peripherals offer a bit more cause for concern. The decline has apparently led to a drop in Corbin’s K-rate. In April, he struck out 55 in 40 innings, a rate of 12.4 per nine innings. For May, the same figure is 10.1, though that’s still comfortably above average for a starter. The walk-rate has gone in the opposite direction, from 1.6 to 2.8 per 9 IP. As a result mostly of those two things, his FIP (expected ERA) has increased from 2.66 to 3.52; he has been helped out in both months by a low batting average in balls on play.
Patrick has been getting fewer swinging strikes, down from 18% of pitches in April, to 11% this month. Interestingly, this decline occurs across all his arsenal - including the slider and curve, where that has been no significant velo change. And when hitters make contact, we see a sharp uptick in quality. For April the hard-hit percentage off Corbin was 33.7%. In May, it increased almost half again to 49.3%, with the line-drive rate going up from 18.8% to 26.0%. However, Corbin’s last outing, in Oakland was his best since the one-hitter: seven innings of one-run ball, with a K:BB of 7:1, and a season-high 23 strikes looking. Perhaps he’s adjusting his approach accordingly? Something to keep an eye on today.