Declining Differentials, Or Why There May Still Be Hope For King Felix

Things do not look good for Felix Hernandez. He is striking out close to two fewer batters and walking close to two more batters per nine than he has over the course of his career. His ERA continues to be excellent at 2.27, but his declining peripherals suggest that Hernandez is no longer the elite pitcher he was over his first 11 seasons. Meanwhile, it’s hard not to believe that his diminished fastball, which at 89.7 average mph has dropped below 90.0 for the first time, is the primary culprit. I’m not telling you anything here you didn’t already know if you have been a regular FanGraphs reader over the last month.

Perhaps I’m nostalgic, but I’m less ready to give up on Hernandez than I have been on pitchers like Justin Verlander who have lost velocity. For Verlander, his fastball seemed to me to be the keystone to his repertoire. His 92.3 career fastball run expectancy (wFB) was 50 runs higher than his next-best pitch. Hernandez’s keystone pitch is his changeup (128.9 wCH), not his fastball (37.6 wFB). Obviously, a pitcher’s success with a changeup depends on his fastball, but the underreported parallel to Hernandez’s declining fastball velocity is his declining changeup velocity. Here’s a leaderboard of the starters with the biggest drops in their fastball-changeup differential in 2016. Hernandez is not on the list.

Biggest Declines in Fastball-Changeup Differential, 2015-16

Player	Differential Change	2015 xFIP	2016 xFIP
Robbie Ray	-2.5	4.03	4.24
Chris Sale	-2.3	2.60	3.55
Mat Latos	-2.3	3.69	4.95
Wily Peralta	-2.1	4.57	4.85
Jake Peavy	-2.0	4.47	4.85
Chris Archer	-1.9	3.01	3.09
John Lackey	-1.8	3.77	3.25
Collin McHugh	-1.7	3.91	4.30
Dallas Keuchel	-1.4	2.75	3.66
Wei-Yin Chen	-1.4	4.01	3.93
Jeff Locke	-1.2	3.94	4.64
Clayton Kershaw	-1.1	2.09	2.00
Sonny Gray	-1.1	3.69	4.13

As a group, these 13 starters have performed worse in 2016 than they did in 2015. Dallas Keuchel and Sonny Gray, in particular, have been two of the most disappointing elite starters this season. Still, it is difficult to identify obvious patterns when you look at yearly changes in isolation. For example, Clayton Kershaw may have lost 1.1 mph of differential between his fastball and changeup this season, but he gained 1.1 mph of differential in 2015. With both changes, he’s right back where he was in 2014.

Hernandez has lost 0.7 mph of differential this season, but that is neither an unusual change for a pitcher nor an alarming decline for him given his career trajectory. Obviously, Hernandez is far removed from his first few seasons when he had a differential of more than 10.0 mph, but he had his current 3.0 mph differential back in 2013 and then pretty much again in 2014.

Felix Hernandez’s Fastball-Changeup Differentials

Season	FA Velocity	CH Velocity	Differential
2005	95.8	85.0	10.8
2006	95.2	84.8	10.4
2007	95.6	86.6	9.0
2008	94.6	87.5	7.1
2009	94.0	89.2	4.8
2010	94.1	89.8	4.3
2011	93.3	89.3	4.0
2012	92.1	88.7	3.4
2013	91.9	88.9	3.0
2014	92.4	89.3	3.1
2015	91.8	88.1	3.7
2016	89.7	86.7	3.0

As his fastball has declined in recent seasons, Hernandez has continued to find success with his off-speed pitches, and that appears to be the case again in 2016. His changeup, curveball, and slider all have positive run expectancies, and his -0.63 fastball run value per 100 pitches is actually improved slightly from -1.00 last season. Meanwhile, there is no change in Hernandez’s hard-contact rate to suggest that batters are having an easier time squaring up his pitches.

There is no cure for the nervousness that fantasy owners will have for Hernandez given his declined velocity, strikeout rate, and walk rate. Frankly, there are not many elite starters whose fastball velocity is below 90 mph. But, if you were going to pick a starter who maybe could do it, you’d pick Hernandez. With many of his owners in fantasy eager to unload him at well below draft-day value because of the obvious warning signs in his peripherals, I’m still optimistic enough to be the buyer.