The modern right-handed reliever probably throws two pitches, a fastball and a slider. You might have a pitcher like Dellin Betances whose slider is a weird slider-curve hybrid, or you might have an Adam Ottavino whose slider looks like a frisbee, but that’s pretty much the prototypical relief pitcher in 2019.
More interesting than the general breakdown of relief arsenals is the trend therein: relievers, the hardest throwers in the game, are throwing fewer fastballs and more sliders. The reasoning behind this is twofold: sliders have by far the most potential to suppress runs, and a batter seeing fewer fastballs means that a velocity increase will be that much more effective.
To the first point, FanGraphs sets a weighted value of runs allowed or suppressed per pitch type, called pitch values. The higher the number, the harder a given pitch is to hit. Sliders have been the most valuable pitch in baseball by far in each of the last five seasons, greatly increasing the incentive to throw them more often.
Fewer fastballs also means that batters will have a difficult time adjusting to an increase in velocity All hitters can eventually catch up to speed — even Aroldis Chapman gives up home runs. If a batter sees three fastballs in succession at 101, he’ll eventually be able to get his timing down. If he only sees one fastball at 101 followed by two wipeout sliders, it messes with his timing more, giving even more advantage to the pitcher.
Now, let’s talk about Chad Green and his pitch usage:
He rode a high spin rate fastball until it didn’t work, bottoming out in a Triple-A stint earlier this year. He has thrown his slider more in 2019, especially in his two appearances since being recalled. Overall, he’s thrown the slider about 20% of the time, but in his last two outings he’s gone to it 28% of the time, and it’s a good pitch:
These are his two appearances this week, with pitches sorted by result. He threw 10 sliders in the two games and got five swinging strikes. Overall he is running a 44% whiff rate on the slider, which would put him among the elite in baseball. For context, Ottavino gets about a 42% whiff rate on his slider, and Betances last year was at 40%. The slider alone has become an elite pitch for Green, and he needs to throw it even more.
Even when batters make contact, it’s been a great pitch. He’s had two sliders put in play since returning from Scranton, both on Friday night. One slider was an easy groundout off the bat of Yandy Diaz, and the other was the very weak single and error to Gleyber Torres. That second ball in play had an exit velocity of just 67 mph and an expected batting average of 0.080. If a pitcher is going to give up contact, that’s exactly what he wants.
This slider superiority becomes especially true when one sees that his fastball is less effective year after year, with whiff rates dropping from 37.9% in 2017 to 27.9% and 22.8% each of the next successive years. His fastball velocity is fine, hovering between 96-98 mph, but when he throws it three times in a plate appearance, the batter will time it.
Green’s slider is better than one would think based on how often he throws it, and if he wants to get back to being the high-leverage reliever he used to be, he has to get that slider usage up. Guys like Betances and Ottavino have similar sliders and throw it 40%+ of the time, and Green needs to copy their example.