In a season marred by injury, Robertson’s curve was the greatest casualty. Dating back to 2013, opposing batters never had a wOBA over .200 agaisnt it while striking out at least 48.9% of the time. A shortened sample (30 pitches thrown) in 2019 saw career-worst 91.4 mph exit velocity and .468 wOBA.
Increasing his cutter usage by more than 10% from 2018 to 2019 did not yield great results for Robertson. Only throwing 72 cutters total, Robertson walked an unbelievable 33.3% of batters. Balls that were actually put in play averaged an exit velocity of 94.1 mph.
Robertson has more or less thrown out his fastball as his career has progressed. He has not thrown the pitch more than 10% of the time for any season since 2013. I don’t expect that to change when/if he returns at some point in 2020.
Robertson introduced the slider to his repertoire in 2017, and it added a new layer to his arsenal. Between 2017 and 2018, Robertson’s slider struck out 24.5% of opposing batters while only allowing an average exit velocity of 85.2 mph.
The cutter was Robertson’s go-to pitch and strike-getter, so when you see the spiked 16.8% walk rate, it’s very concerning. Add to that a career-high HR/FB rate of 22.7% and you can see clearly that his cutter struggled when left center and down in the zone.
Robertson’s hammer knuckle-curve comes in hard and fast, and it’s a deadly weapon in his arsenal as a two-strike pitch. He wiped out 44.4% of batters with a strikeout on the pitch and only allowed an impressive .142 batting average against. As long as he keeps the pitch down, he gets a ton of chases, and a low zone rate won’t hold him back.
The slider is really the third offering that rounds out Robertson’s repertoire. Because it sits within 1 mph of his curveball yet has 13 inches less of a vertical drop, it serves to as a good way to keep hitters off balance. This means he gets some chases and a few whiffs on the pitch. As long as he keeps low on the pitch, he fares well, as evidenced by his very impressive .107 batting average against last season.