Six MLB pitchers who have taken a step backward in 2019

Edwin Diaz, New York Mets

If Blake Treinen was baseball’s best reliever last year when looking at fWAR and ERA, Edwin Diaz wasn’t far behind. The right-hander owned a 1.96 ERA, 3.5 fWAR, and led the league with 57 saves. But through 52 innings in 2019, those numbers are sitting at 5.88, -0.1, and 25, respectively.

The following tweet is a few days old, but it still hits home with just how much Treinen and Diaz have struggled as a unit this year:

Edwin Diaz and Blake Treinen combined last year:
153.2 IP, 23 ER, 7 HR, 37.7% K, 6.4% BB, 1.35 ERA

Edwin Diaz and Blake Treinen combined this year:
107.1 IP, 62 ER, 22 HR, 29.2% K, 11.3% BB, 5.20 ERA

— Jeremy Frank (@MLBRandomStats) September 4, 2019

Although they’re a step down from last year, Diaz’s swing-and-miss numbers are still strong — he owns a 38.5% strikeout rate and 17.6% swinging-strike rate. The problem is that when hitters make contact, the results have been devastating. He limited his opponents to 0.61 homers per nine innings and a 29.3% hard-hit rate last year, but those numbers have skyrocketed to 2.42 and 49.2% (!) in 2019.

Diaz has encountered problems with both his fastball and slider, but his slider is what’s really hurting him because that’s where he’s historically done most of his damage. The opposition produced a 21 wRC+ and 56.4% strikeout rate against that offering in 2018. This year, they’ve posted a 144 wRC+ and just a 34.3% strikeout rate.