Closer Edwin Diaz has appeared in 11 games so far this season while completing all nine of his attempted saves and absolutely baffling hitters. It’s been fun to watch the third year veteran dominate opposing lineups, but where’s the success coming from?

Let’s take a look.

Through his first 10.1 innings, Diaz has reduced the rate that he’s using his fastball usage from his previous seasons in the big leagues while increasing his slider usage.

This change in his pitch usage has resulted in predictable increase in number of strikes that are swung and missed at inside the strike zone — it’s currently at a career high of 19.6%. As the whiff percentage has increased, so has Diaz’s K/9 ratio (16.55) which has led to the batters he’s faced earning a ridiculously low batting average of .056; the low batting average is aided by the fact that opponents are posting a BABIP of .133 throughout the season.

By increasing the usage in his slider, Diaz’s has increased his unpredictability and it’s made it harder for batters to predict what’s coming there way. In the below .gif, watch the weak contact the 24-year old induces because the batter is behind on the fastball.

Jean Segura ends the game with a great over his shoulder catch and the Mariners beat the Giants 6-4 #GoMariners pic.twitter.com/x79t609Fyh

— Lookout Landing (@LookoutLanding) April 3, 2018

What’s interesting to note is that he’s inducing less swings at pitches outside of the strike zone than he has in the past (30.3%) while inducing slightly more swings at pitches outside of the zone (68.0%). The reason for this decrease is it seems Diaz has been throwing more pitches inside the strike zone this season than he had in his previous full season.

Compare his (above) 2018 heatmap to the (below) ’17 one.

It’s interesting to see that he’s currently feasting more on the lower right corner of the zone than he had last season. If he continues to pick on the corner of the plate with the difference in velocity between his pitches…it’s going to induce a lot of silly swings and ground balls. That high ground ball (53.3%) and strikeout rate has been why Diaz has been able to strand 90.9% of batters that have managed to reach base.

This means that Diaz has been Seattle’s most valuable pitcher throughout the first month of the season (0.4 wins) while pitching 0.79/1.85/2.39 and securing 75% of the team’s 12 wins.

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