Affectionately known as “Sugar” by his teammates and friends, Mariners reliever Edwin Diaz is a man worthy of a different nickname. It’s not that “Sugar” is bad, it’s just that there really isn’t anything sweet about what Diaz does on the mound. Beneath his gleaming teeth and broad smile there lies an absolute killer. I can only imagine what hitters must feel when they look at the mound and see that Diaz is staring back at them. He slowly widens his smile, until every single one of his pearly whites are on display. That has to be the moment; the moment when the hitter knows that Diaz is a velociraptor reincarnate.

The talent has always been present for Diaz, and it has been recognized by many. Back in 2014, Baseball America named him the fourth-best prospect in Seattle’s organization. The Mariners were a top-heavy prospect organization, lacking in much depth. But a player like Diaz stood out among his fellow top prospects. The Mariners envisioned big things for Edwin Diaz; a dominant starter for years to come.

When Diaz was drafted in the third round of the 2012 MLB draft, he was a fireballer with lots of upside. As he made his way through the Mariners minor league system, he worked on developing a slider and would occasionally mix in a changeup. The fourseam fastball remained his weapon of choice, and when one can get said fastball up to 102 miles per hour, it made sense for that to be his go-to pitch. The problem for Diaz rested on his mix-up pitch, the changeup. To put it bluntly, it’s never been good. At best it’s average, and at its worst it is extremely hittable. This made Diaz a two-pitch pitcher, which also meant that against big league pitchers he would most likely struggle pitching multiple innings every fifth day.

Realizing how dynamic Diaz’s fourseam and slider were, the Mariners made the decision in June to bolster their relief depth at the big league level. Diaz, who had already started appearing in relief roles for the Jackson Generals, was called up to the big league club. He left his changeup behind, as according to Brooks Baseball he has thrown his change to a tune of 0.12 percent of the time (which correlates to a grand total of having thrown it once) with the Mariners. Diaz has for all intents and purposes become a two-pitch pitcher and the Mariners have to be pleased as pie with the results.

Diaz’s fourseam is his set-up pitch and it is the pitch he rides hard. He throws it 67 percent of the time for a whiff percentage of 12. He manages to regularly sit at 95 to 97 miles per hour with the fourseam. It is, however, his slider that has proven to be devastating. His slider is around 87 to 90 miles per hour, but he gets nasty movement on that pitch. Diaz uses the slider 32 percent of the time, and batters whiff on it at an astounding 35 percent rate. There’s a hammering away at the door effect to what Diaz does with his two pitches. He punches away with the fastball, and then he finally knocks the door down with the big hammer of a slider he possesses.

At first Diaz did this as a reliever, and then a set-up man. That is until an injury to Steve Cishek opened the door for Diaz to assume the closer’s role. Once he assumed it, Diaz never looked back. He racked up save after save, and strikeout after strikeout. In August he was nearly untouchable as opponents were only able to bat .250 off of his fourseam and .095 off of his slider. The young man from Puerto Rico had arrived and the world was his oyster, or so it would seem.

September was not as kind to the Bakersfield Blaze farmhand. He began to rely on his slider even more, up to a 42 percent usage rate. He was still generating a lot of whiffs, but the more he broke it out the more contact was being made. In July his slider had a whiff percentage of 42, but with increased usage, the whiff percentage dropped to 32 in September.

Now, before the pitchforks come out, I understand that a whiff percentage of 32 in any month is terrific. But there is some cause for concern with how batters have been slowly adjusting to his slider. That batting average against of .095 that I raved about in August; it jumped up to .222 in September. Again, that’s not a bad total by any means. But, in addition to the blown saves and the possible trouble with working multiple innings that sprouted up in September, his devastating pitch was hit a heck of a lot more.

In the end, I think Diaz will be fine, because if nothing else he’s simply regressed more towards the mean. His slider is still devastating and he can still bring the heat with his fourseam. The changeup has been completely forgotten, which is for the best. But with those two pitches, and if Diaz can maintain his velocity and movement, the Mariners may have found themselves something special in their new closer of the future. Behind that gleaming smile is a lot of talent, and a velociraptor just waiting to pounce on his next victim.