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As he refines arsenal, Nats’ Mason Thompson could become bullpen mainstay

Mason Thompson finished the season strong with 12 scoreless outings in his final 15 appearances. (Katherine Frey/The Washington Post)

The Washington Nationals started their roster teardown at the 2021 trade deadline knowing that not every player they acquired would ultimately pan out. But the hope was a few would show promise and fit into the team’s future.

One of the players acquired at that deadline two summers ago, right-hander Mason Thompson, has shown flashes that he could become a mainstay in the bullpen — if he continues to refine his arsenal and improve his command. Washington received Thompson from the San Diego Padres along with infielder Jordy Barley for Daniel Hudson. After getting a look that season, Thompson, 24, followed it up with a 2.92 ERA in 24 games in 2022.

He slotted into a bullpen constructed of hard-throwing relievers who performed above expectations for Washington this past season. And after suffering an early-season injury and being optioned several times, he finally found his footing.

“We all got to compete together and somewhat in a way compete against each other,” Thompson said in September. “Just try to make everybody better and hopefully put the best result out there on the field.”

The Nationals added Hunter Harvey and Carl Edwards Jr. last season. Both players dealt with a slew of injuries early in their careers but became strong end-of-the-bullpen arms for Manager Dave Martinez. And the Nationals already had Kyle Finnegan and Tanner Rainey, the team’s closer until he suffered a UCL strain in July.

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This offseason, Washington could follow a similar formula to last season, when it claimed Harvey off waivers and signed a motley crew of relievers in Edwards, Victor Arano, Jordan Weems and Erasmo Ramírez to minor league deals. It kicked off this offseason by signing longtime National Sean Doolittle to a one-year deal, with the veteran left-hander coming off an internal brace procedure in July. The Nationals also agreed to a minor league deal with Hobie Harris this month.

Or they could stick with their current cast of characters, which includes Thompson, to find out who flashes long-term potential. Thompson, Weems and Andrés Machado finished the year in the majors after bouncing between levels. Arano had strong moments when healthy and could be another arm out of the bullpen. Matt Cronin, who was protected by Washington from the Rule 5 draft this month, could get a shot with a Nationals bullpen that desperately needs left-handed arms. He finished the season with Class AAA Rochester.

Thompson made the Opening Day roster before being placed on the injured list with a biceps strain after just his second appearance of the season. Once he returned from the injury in July, he was sent down twice before sticking in September.

From Sept. 1 to the end of the season, he recorded scoreless outings in 12 of his final 15 appearances. He recorded his first career save Sept. 5, a three-inning outing against the eventual NL Central champion St. Louis Cardinals, who featured a lineup that included MVP Paul Goldschmidt and runner-up Nolan Arenado. Not to mention he had to retire Albert Pujols twice as the legendary slugger chased his 700th home run.

Thompson threw more strikes this year, leading to his improved numbers from the previous season. But he also credits his growing confidence in his slider, which he threw 23 percent of the time a year ago, a jump from 13 percent. Thompson admitted to trying to force the pitch in 2021 to create a sweeping slider like he saw from some other pitchers.

The vertical movement on Thompson’s slider would have tied him for 95th among qualified pitchers who threw sliders this season had he pitched enough games. The horizontal movement on the same pitch would rank him tied for 245th.

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“I would look at the numbers, and I’m like, yeah, maybe it’s just not a good pitch because it doesn’t have the 15 inches [of movement] going [away from the hitter],” Thompson said. “So I think for a while I was trying to make it do more, and finally I got to the point where I’m like I’m throwing it, they’re getting swings and misses or weak contact, it’s obviously working.”

Batters hit .067 against his slider and whiffed 51.4 percent of the time when he threw the pitch. With his slider and sinker — his primary pitch — plus the potential addition of a refined change-up, Thompson believes he can have three effective pitches next year. But that means nothing if he struggles with location, which was the primary reason for his demotion when he returned from injury.

A puzzling aspect of Thompson’s outings this year was his strikeout numbers; he averaged only 5.47 strikeouts per nine innings. The major league average is 6.93 — a curious disparity for a hard-throwing reliever.

Thompson said he wants to work on finding ways to put batters away when he’s ahead with two strikes with better pitch sequencing, but he also said he doesn’t harp on the strikeout numbers as he might have in the past — as long as he’s getting outs.

“This day and age, of course everybody wants to get a strikeout,” Thompson said. “And for me, I’m going to continue to attack guys. And if I can get an out on the first, second, third pitch of the at-bat [and] the guy’s going to roll it over to shortstop, I’ll take that all day long. … As a pitcher, that’s all you can really ask for.”