Diaz has an elite fastball in terms of velocity sitting at 97 mph but he struggled to contain the long ball this season giving up 9 homeruns, the most of his career, which can be explained by the awful HR/FB ratio of 32%. It’s not all bad though as batters had a lower contact rate this year at 68%, a drop of 6% from his previous low. Looking forward, he’ll need to focus on limiting the flyballs by keeping the ball lower in the zone.
Just like his fastball, Diaz’s slider had a very bad HR/FB rate of 35% which in terms led to doubling his homerun total from last year to 6 despite throwing it 75 fewer times. However, it went in the opposite direction than the fastball in terms of contact%, finishing the season with the highest rate of his career at 58%.
Diaz’s fastball had earned just a 0.7 career pVal entering 2018, his 2.2 in 2017 representing a career high until blowing that out of the water with a 13.8 pVal in 2018. He maintained the 0.5 mph increase in fastball velocity from 2017 and added just over 50 RPM in spin rate, contributing to a career-best 32.9 K% with the pitch. Also of note is that the difference in horizontal release point of his slider and fastball were by far the closest they’ve been in Diaz’s career, making the two pitches significantly harder to read out of Diaz’s hand.
Diaz’s slider has always been a spectacular pitch for him, but when combined with the highest number thrown as well as a vastly improved fastball, he got by far the best results of his career. As it always has been, the slider was Diaz’s putaway pitch, with 75 of his 124 punch outs coming via the slider. Contributing to this were career bests in velocity, spin rate, zone swing rate, and a 1.5-inch increase in vertical movement on the slider from 2017 to 2018.