Travis Sawchik at 538 crunches the numbers:
"The Milwaukee Brewers reliever has struck out an absurd 50 percent of batters faced this season.1 For a single season in the pitch-tracking era,2 only two pitchers have posted higher rates: Aroldis Chapman at 52.5 percent in 2014 and Craig Kimbrel at 50.2 percent in 2012.
But what’s perplexing about Hader’s whiff rate is that hitters know what’s coming: He is going to throw his four-seam fastball. Hader turns to his signature pitch on 88.6 percent of his throws, a greater frequency than all but two MLB pitchers to have thrown at least 20 innings this year. While the pitch’s velocity (95.9 mph) is above average, it ranks just 66th among fastballs. By comparison, Chapman’s fastball averages 98.2 mph, which is sixth-best in the league.
Hader also owns a below-average total spin rate, as calculated by Statcast’s TrackMan Doppler radar component. The average spin rate for a four-seam fastball this year is 2,284 revolutions per minute, while Hader’s is a rate of 2,154 rpms. Moreover, fastballs — even mid-90 mph iterations — are generally pitches that produce some of the lowest swing-and-miss rates in baseball.
Yet batters are whiffing on 44 percent of their swings against Hader’s fastball, the top mark in the majors.3 Another 40 percent of swings against his fastball are fouled off — meaning that an opponent is able to put a ball in play just 16 percent of the time he swings at a Hader fastball. Opponents are batting just .132 against the pitch."
