Aroldis Chapman is a pitcher, not a thrower

Aroldis Chapman brings more to the mound than a blazing 100+ mph four-seam fastball. While Chapman's heater provides the foundation for his dominance closing out games, he features a three pitch repertoire that he deploys according to the count and whether he is facing a left-handed or right-handed batter.

The pitches: fastball, changeup, slider

Chapman employs a four-seam fastball, a changeup, and a slider to challenge opposing batters. According to Brooks Baseball, in 2015 Chapman threw his four-seamer just over three quarters of the time (76%), at an average velocity of 100.4 mph, with slight tailing action away from right-handed batters.

His slider is his second-most frequently utilized pitch, which Chapman threw approximately 17% of the time during the 2015 campaign. Chapman's slider has an average velocity of 89 mph, and cuts in on the hands of right-handers.

Chapman began throwing a changeup during the 2014 season.  In 2015 he utilized his changeup about 8% of the time.  Chapman's changeup sits about 11-12 mph beneath his fastball in terms of velocity, averaging 89 mph with movement that tails away from right-handed batters.

Although Chapman's fastball is his featured pitch against both righties and lefties, his approach differs quite a bit depending on the side of the plate that the opposing batter is occupying.

Lefties versus righties

Against left-handed batters, Chapman is essentially a two-pitch pitcher, all but doing away with his changeup except very occasionally when is he is ahead in the count or has two strikes. Chapman relies even more heavily on his fastball against left-handers, deploying it 81% overall, 88% as a first-pitch, and 87% of the time when the batter is ahead in the count. Chapman turns to his slider more frequently against lefties when he is even (17%), ahead of the batter (22%), or has two strikes (18%).  In short, against left-handed batters, the name of the game for Chapman is to get ahead with his fastball, and put the batter away with his slider.

Against right-handed batters, Chapman alters his approach to incorporate his changeup. Chapman uses his changeup about 12% of the time overall against right-handers, and deploys the pitch most frequently as a first-pitch (12%), when he is ahead in the count (18%), and when he has two strikes against the opposing batter (10%).

The inclusion of a changeup in his repertoire against right-handed batters means that Chapman throws fewer fastballs overall against right-handers (74%) than he does against left-handers (81%). This drop-off is most noticeable on first-pitches, when Chapman only throws his fastball 69% of the time (versus 88% of the time against left-handers), or when he is otherwise even in the count (67% against right-handers versus 83% against left-handers).

In these first-pitch and even count circumstances, Chapman turns to his slider more often as a way of getting inside and jamming right-handed batters. He uses his slider less frequently as a put-away pitch against right-handers, turning more often to his fastball or changeup when he is ahead in the count or has two strikes.

The results

Despite the differences in Chapman's approach to right and left-handed batters, the results are one in the same: dominant. About 72% of the plate appearances against Chapman in 2015 were by right-handers, and he held them to a staggering .297 on-base, .257 slugging, .554 OPS, yielding 34 hits, and just 45 total bases. All three home runs that Chapman gave up in 2015 came against right-handers, while he struck out 3.55 right-handed batters for every one that he walked.

Opposing teams were wise to avoid sending left-handers against Chapman. They reached base nearly 28% of the time (.276 OBP), while slugging .175, for an overall OPS of just .451. There were just nine left-handed hits against Chapman in 2015, for a total of 11 bases yielded via hit over the duration of the entire season.

I share many of the reservations expressed on this website and elsewhere regarding the Yankees' acquisition of Chapman. Sports fandom is much more enjoyable when you feel good about the players and coaches you pull for as human beings. However, from an analytical perspective, Chapman is fascinating to watch not only because of his electric left arm, but because of the approach he takes to the mound that is adaptable to both the batter he is facing and the count. Make no mistake, Chapman is a pitcher, not a thrower. And it is that pitching ability, in addition to his three-digit fastball, that make him the dominant bullpen force in Major League Baseball today.