Diaz has great velocity on his fastball, but struggled with it this year as he allowed eight extra-base hits in 58 at-bats, which resulted in a wOBA against of .379. He’s always been fairly good at containing the fly balls on his fastball (never been over 24%) but this year that number jumped to 32%, a trend he does not want to see continue now that he will be pitching quite a few times at Coors Field.
Diaz’s slider was by far his best pitch, and quite frankly, should be grouped with the top pitches in the league, as it generated a whopping 47% whiff rate along with a .189 BAA and .234 wOBA against. This high whiff rate can be attributed to its vertical movement as he is able to generate 4 inches more than league average. He seems to have worked on generating more drop than lateral movement, as he sacrificed 3 inches of horizontal break from his last season in 2017 in order to gain 7 vertical inches.
Diaz had average movement on his four-seamer, and could crank it up to 100 mph when he needed to. Considering this, it’s a bit surprising how much contact it gave up, and how much it struggled to produce whiffs. Opponents went 11-for-18 against it in 2017.
The slider had good cut, but below-average drop to it. It was thrown less than 30 times on the year. Every batted ball against the pitch was hit on the ground.