ST. PETERSBURG -- The Rays surprisingly parted ways with high-leverage reliever Diego Castillo on Thursday, trading the right-hander to the Mariners for righty reliever JT Chargois and infield prospect Austin Shenton.

The deal comes at an unexpected time, as Tampa Bay is currently without several of its best relievers, but general manager Erik Neander’s logic behind it was pretty clear. The Rays believe Chargois is a reliever on the rise, with less history than Castillo but similar traits, and the potential of Shenton made up for the risk they assumed in taking on the less proven arm exchanged in Thursday’s deal.

“There’s a difference in track record, what’s behind these guys, but when we’re looking at what’s ahead of JT, we have a lot of confidence that he’s going to be a big part of this group moving forward,” Neander said on a conference call with reporters Thursday night. “The price for taking on the risk of the different backstory and the history is why we got Shenton, whom we’re high on.”

Castillo will fill a need for the Mariners, giving them a controllable closer to replace the recently traded Kendall Graveman. But his departure seemingly creates a temporary hole for the Rays, who were thought to be pursuing pitching prior to Friday’s 4 p.m. ET Trade Deadline.

It’s possible the Rays will make more moves to shore up their injury-riddled bullpen in the coming hours, of course. Neander said he and his baseball operations staff will be “plenty busy” looking for opportunities to improve the Rays’ roster, though he acknowledged their “big move” already took place last week with the acquisition of designated hitter Nelson Cruz.

The decision to trade Castillo came as somewhat of a surprise given the win-now nature of the Cruz deal, but more so because of the current state of the Rays’ bullpen. They currently have 14 pitchers on the injured list, with Pete Fairbanks joining that group on Thursday morning, leaving Castillo and All-Star Andrew Kittredge as their top active high-leverage arms. 

Castillo has seen his average sinker velocity dip from 98.2 mph in 2019 to 94.8 mph this season, but he remained one of Tampa Bay’s most reliable relievers with a 2.72 ERA and 49 strikeouts over 37 outings this season. The 27-year-old right-hander recorded a 1.66 ERA during the regular season and a 1.64 ERA in 10 postseason appearances last year, and Neander praised Castillo for a successful four-year Rays tenure with “as many big outs as anybody, as slow a heartbeat as anybody, as good a person and a professional as anybody.”

But the Rays are optimistic about the late-inning options they’ll have when relievers like Fairbanks, Nick Anderson, J.P. Feyereisen, Collin McHugh and Ryan Thompson return in the coming weeks. (They are all currently on the IL, and Tampa Bay hasn’t set a projected return date for any of them.) And the 30-year-old Chargois (pronounced “SHA-gwah”) seems likely to take on some high-leverage bullpen work as well, based on the Rays’ evaluation of him.

“We have a lot of confidence in Chargois moving forward here, think he’s going to step right into our group, be a really good contributor for us, and hopefully his best days are ahead of him,” Neander said.

After spending last season in Japan and joining Seattle this year on a Minor League contract, Chargois has broken out with a 3.00 ERA with 29 strikeouts in 30 innings over 31 relief appearances for the Mariners this season. 

His slider is his primary pitch, accounting for 69 percent of his offerings this season -- the fourth-highest usage rate in the Majors behind one current Rays reliever, Matt Wisler (90 percent), and Castillo (70.4 percent) -- and he throws a sinker that averages around 95.8 mph. Neander acknowledged that Chargois has an arsenal that is “not all that different from Diego,” another pitcher who gets strikeouts and ground balls with heavy sinkers and wipeout sliders, and seems to be improving.

“So much about the ‘pen in a given year is how you’re throwing the ball at present and finding success, and this is someone that’s really finding Major League success really in this way for the first time. The confidence that comes with that can be a powerful thing,” Neander said. “We’re seeing the fastball command, in our opinion, improve through the course of the season, and we’re seeing him really find his breaking ball – not just the shape and the power of it, but the command of it.”

The 23-year-old Shenton, a left-handed hitter, is batting .300/.414/.566 with 29 doubles, 12 homers and 61 RBIs in 67 games between High-A Everett and Double-A Arkansas this season. He has started 45 games at third base, 15 at first base, four at designated hitter and three at second base this season, and he’s also played both corner-outfield spots.

Shenton was the Mariners’ No. 17 prospect, according to MLB Pipeline, and he joins the Rays’ top-ranked system as their No. 22 prospect. A fifth-round pick by the Mariners out of Florida International University in 2019, Shenton has consistently shown the ability to hit with a mature approach and consistent hard contact at the plate.

“He has really hit. Some feel for contact. Some feel for power,” Neander said. “[He has] a pretty good chance to be a big league contributor -- and not terribly far off from doing that. A player we like. For us, it was worth acquiring Shenton for the difference in track record between the two Major League relievers that were exchanged.”