Rookie relief pitcher Dominic Leone has earned a spot in the Seattle Mariners bullpen and could soon be moving into a more critical role for the team.

Since making his debut April 6, the 22-year-old right-hander has excelled as yet another power arm in Seattle’s bullpen. In 19 appearances, Leone has a 1-0 record with a 1.57 ERA and the peripheral statistics to suggest he should be able to continue pitching at a high level.

For a number of reasons, Leone has been used often as a long relief man or in mop-up duty. But he’s now ready to step in to a larger role and pitch in more high-leverage situations.

Leone was selected by the Mariners in the 16th round of the 2012 draft and quickly became a highly touted pitching prospect, reaching Double-A Jackson in less than a year. A starter at Clemson, the Mariners figured Leone’s fastball-cutter combo would be better suited for a bullpen role and converted him to a closer in the low minors.

They were rewarded for that decision, as Leone cruised through his first three stops, running strikeout rates around 30 percent along the way. He reached the High-A level early in 2013 and held his own with a 2.50 ERA and two home runs allowed in 29 games at hitter-friendly High Desert.

Part of Leone’s success has been thanks to increased velocity on his fastball. Early on in his career, Leone’s velocity would range between 90 and 92 miles per hour. At High Desert, he was suddenly sitting in the mid-90s and touched 97 at times, which he continues to do in the majors.

Leone talked to George Alfano of last year about his bump in velocity, crediting it to improved mechanics.

“I keep a consistent approach,” he said. “If you do that, the strikes will come and you’ll keep the ball down. I keep my motion fluid and my arm is getting on top.”

Leone reached Double-A shortly after and skipped the Triple-A level altogether. He was called up when Hector Noesi was designated for assignment April 6, marking yet another incredibly fast riser in Seattle’s organization.

Since then, Leone has been strong out of the bullpen and is rewarding the Mariners for rushing him through the minors. Leone’s ERA ranks 11th in the American League among relievers, bolstered by an 8.1 inning-long scoreless streak throughout most of May.  

Leone is also running an impressive strikeout rate of 27.7 percent, adding yet another powerful arm with high strikeout potential to Seattle’s bullpen. He struck out five while allowing just one hit and no walks in 2.1 innings in his most impressive outing of the year May 14 against the Tampa Bay Rays.

As it was during most of his minor league career, Leone’s most valuable pitch has been his cutter. Per FanGraphs, opposing hitters have swung and missed at the pitch 13.3 percent of the time and have only made contact at a rate of 72.5 percent.

Leone’s slider needs a bit more refinement, but it is developing quickly. He has successfully mixed in his slider on just over 19 percent of his pitches and is continuing to get better command with the pitch.

As you might expect with a pitcher two years removed from the draft, Leone’s biggest issue has been his control. Leone’s walk rate of 9.6 percent is a bit higher than you’d like to see after he struggled a bit with throwing strikes in April.

But Leone is quickly improving with that aspect and has only walked one batter over his last seven appearances. Fellow reliever Tom Wilhelmsen praised Leone’s recent approach of aggressively attacking the strike zone, via Greg Johns of

He’s kind of the leader by example right now. He’s doing pretty darn well for himself. He just gets in and shows strike one, strike two and is just a bulldog. He goes right after you. He’s truly fun to watch. I’m just trying to follow Dom’s lead.

Despite the instant success, Leone has mainly been used as a long reliever. He’s gone over two innings in five different appearances and has rarely been used in the late innings of close games.

That has mostly been out of necessity. The Mariners don’t really have another pitcher for long relief and the team has needed one pretty much every time Brandon Maurer has started.

But that could be changing in the next month. Taijuan Walker and James Paxton are hoping to join the team sometime in June and will be taking over two rotation spots when they do, altering the dynamic of Seattle’s bullpen.  

That is likely going to bump Chris Young out of the rotation. However, Young has pitched well enough to earn a spot on the team, particularly at Safeco Field, as Shannon Drayer of 710 ESPN points out.

Young is an ideal fit for that long relief role, potentially freeing up Leone for some more high-leverage situations.

Obviously, Leone won’t instantly become a closer or primary set-up man. But he does have enough ability already to be the third guy out of Seattle’s bullpen and set up Fernando Rodney whenever Danny Farquhar needs a day off.

Giving the inconsistent Yoervis Medina or Wilhelmsen’s innings to Leone is only going to improve the team. Leone has the most upside of anyone in the bullpen other than Farquhar and is getting better with more experience as a pro.

Just two years removed from the draft, Leone is already ready to step into a critical role in Seattle’s bullpen. He can improve the Mariners at the present moment while also being groomed as a potentially dominant reliever in the future.


All stats per FanGraphs unless otherwise noted.

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