Though his strikeout numbers were still elite and he flashed unhittable stuff at times, Mets reliever Edwin Diaz had a nightmarish first season in Queens as his location betrayed him far too often as he gave up 15 home runs and posted a 5.59 ERA.

Part of what ailed Diaz in 2019 was his inability to harness his slider, but his fastball also found way too much plate. And new Mets pitching coach Jeremy Hefner is working on fixing both of those issues after diagnosing the problems.

"Edwin got in trouble with a little bit of arm-side run to his fastball and it ended up finding a few more barrels than he was used to in his career," Hefner said Wednesday night during an appearance on Baseball Night in New York: Living Room Edition. "And so that's all we've been trying to do is straighten out his fastball so he can get it to his glove side more consistently. There's a grip adjustment in there, there's an intent adjustment in there, and there's also some physical, mechanical adjustments in there as well."

As far as the slider, Hefner talked about "adding a little more depth" to it.

"His number one pitch is his fastball and then his slider is number two," Hefner said. "But if we can elevate the slider it'll help his fastball as well. So that's the plan with him."

When Hefner referred to "elevating" the slider, he of course meant making it better, not having it higher in the zone, where it was far too often in 2019.

A look at Diaz's advanced numbers from last season show that if he can improve his location, he should hopefully be able to return to form.

And with Hefner talking about too many balls getting barreled up, here are some examples...

Diaz allowed hitters to barrel up his pitches 10.1 percent of the time (bottom 8 percent of the league) after allowing a barrel percentage in 2018 of 3.8 (top 6 percent of the league).
While Diaz's fastball was a problem in 2019, his slider was an absolute mess, as batters had a .622 slugging percentage against it after slugging .234 against it in 2018.
The above added up to a hard hit rate allowed of 45.3 percent, which was in the bottom two percent of the league.

If and when the 2020 season gets underway, the Mets will hope that Diaz can put the mess of 2019 behind him while implementing and succeeding by using the advice from his new pitching coach.

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