2019 Season in Review - Edwin Diaz

After a lights-out 2018 campaign, Edwin Diaz emerged into the elite class of closers heading into the 2019 season. He wrapped up his historic year with the second-most saves in a single season (57) to go along with a sparkling 1.96 ERA, 0.79 WHIP, and 44.3% K-rate. The Mariners sold high on their young hurler in the offseason by shipping Diaz from the peaceful Pacific Northwest to the bright lights of New York City to play with the Mets. The acquisition, however, turned out to be somewhat of a regrettable move for the National League club.

Getting selected as the top reliever off the board at an ADP of 51.5 in fantasy drafts last season, calling Diaz a letdown in 2019 would be an understatement. In his first taste of full-time NL action, he wrapped up a hideous campaign by cutting more than half off his save total (26) while sporting a 5.59 ERA and a 1.38 WHIP. The only bright spot was that Diaz could still strike out batter's to a 39.0% K%, good enough for fifth-best in the league.

The 25-year-old's free-fall from the upper echelon of relief pitchers forced the Mets to remove him from the ninth-inning role as the team surprisingly stayed in the playoff hunt until mid-September. Where did it all go wrong for Diaz in 2019? Let's dive into the data to help us understand his frustrating year.

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A Diaz-strous 2019

We'll start with one of the few things that went well for Diaz in his debut season as a New York Metropolitan, and that was his ability to strike batters out. To go along with his elite K-rate, the right-hander once again impressed with a 17.8% SwStr%, which was 1% lower from 2018, but still right on his career average. He achieved this top-five number with his slider making batters whiff 43.2% of the time, while his four-seamer improved nearly 5% in this category from 2018 to a 35.1% Whiff%.

Diaz has a two-pitch arsenal, which is common for relievers, but hitters took advantage of their 50/50 shot at guessing what delivery was coming last year. His slider was always an effective pitch for him through his first three big-league seasons, but he struggled with it in 2019. Coming into last season, he held batters to a lifetime .134 BA with five homers off this breaking ball, including limiting them to a .121 BA in 2018. In 2019, hitters punished this offering to a worrisome .297 average while smacking six balls out of the park.

Diaz's slider is still electric and can make batters miss as good as anyone in the league when it's utilized properly. The problem was he threw it in the zone more often than ever before in 2019, with it significantly jumping from a 34.3% Zone% in 2018 to 42.5% last season. In turn, his Whiff% on his slider in the strike zone spiraled from 37.2% in 2018, to a career-low 27.3%. His slider works best when it paints the corner or falls out of the zone, but his command of the pitch failed him.

His struggles with this delivery helped force his HR/9 to balloon from a 0.61 mark in 2018 to a disastrous 2.33 HR/9 last season, the highest number of all relievers. Meanwhile, Diaz' HR/FB doubled from his 13.2% lifetime mark to 26.8%, while he saw his batting average against also hit a career-worst .254. Statcast recorded his expected batting average (xBA) at .200, so there is some optimism since he was on the wrong end of the good luck charm.

The former All-Star also surrendered the second-highest BABIP among all pitchers (.377) after entering the season with a .291 lifetime mark. BABIP doesn't factor in home runs, so this number is a bit inflated even with his general struggles. It was no coincidence that Diaz's 3.07 xFIP and 2.63 SIERA suggested he should have only allowed nearly half the amount of runs. Still, misfortune and home run susceptibility are two dangerous chemicals to mix.

2020 Outlook

Diaz's defined role heading into 2020 remains up in the air after a late-season demotion last year. The Mets will undoubtedly give the Puerto Rican the first crack at the closing job to help justify sending away a promising prospect haul, but it's up to Diaz to maintain the job. Mets GM Brodie Van Wagenen made it clear he won't ship the reliever away, but that doesn't eliminate the possibility that they add an end-of-the-bullpen arm this offseason as a security measure.

Diaz has clued in on his struggles with the slider and is making a point of refining it before spring training begins in February. "The slider's the most important pitch," stated Diaz. "The main goal is just to get that right again so I can be effective." He plans to throw more bullpen sessions this offseason in an attempt to recover his previous success that made him one of the most feared closers in the game.

It'll surely be something to monitor this spring whether or not Diaz can regain his dominance from previous years with this pitch. He'll likely come into the upcoming fantasy baseball season at a price in the mid-to-high 100s for ADP, creating a potential pick for an incredible value. The risk will come with it as well, but even if Diaz can get back to 80% of his 2018 results, he can be a top-five reliever at a top-15 price.