On Sunday, the Red Sox announced they were promoting top prospect Rafael Devers from Triple-A and inserting him as their starting third baseman, filling a spot that had been a pretty big problem for the team this year. Last night, Devers made his Major League debut in Seattle, drawing a pair of walks off of Felix Hernandez and Edwin Diaz. But while Devers was playing his first Major League game, the Red Sox acquired a guy who might end up taking his job.

The deal is as follows.

Boston Receives Player Position Age 2017 WAR Rest of Season WAR Contract Eduardo Nunez 3B? 30 1.1 0.7 Free Agent After 2017 ROS WAR is based on ZIPS/Steamer projection and assumes 232 PAs.

San Francisco Receives Prospect Position Age Level Prospect Rank Shaun Anderson RHP 22 High-A Honorable Mention Gregory Santos RHP 17 Summer League N/A Prospect Rank is based on Eric Longenhagen’s pre-season team write-ups.

In Nunez, the Red Sox pick up a decent enough third baseman. Nunez is certainly no star, but he’s turned into a league-average hitter and he has experience at most of the positions on the diamond. If Nunez was a good defender, he’d be one of the league’s better super-utility guys, or a poor man’s Ben Zobrist.

He’s not a good defender, though. In fact, he’s been kind of terrible everywhere he’s played. He came up as a shortstop but saw his time there diminish after one of the worst defensive seasons we’ve ever seen. Interestingly, UZR and DRS don’t really like him much better at second or third, and he’s graded below average in nearly every year of the Fans’ Scouting Report.

This isn’t one of those times where the data and the scouting reports really disagree either.

When Nuñez made 4-run error earlier, Red Sox scout wrote "YUCK" on his report. https://t.co/hISK2PAeq7 — Andrew Baggarly (@extrabaggs) July 25, 2017

But Nunez hits and runs well enough that even below-average defense makes him a decent enough player. He’s been worth +5 WAR since the start of the 2015 season, and if he’s forced into regular work because Devers flops, he’ll be better than what the team was rolling out at third base before. And if Devers doesn’t flop, and he ends up as a part-time player, there are worst things for contenders to have on their bench than a high-contact utility infielder who can steal bases at a high rate of success.

That said, there’s some risk in Nunez’s profile as well. He’s a free-swinger who doesn’t strike out because he’d rather make contact with a pitch out of the zone than work the count, but he lacks any real power, so his offensive game is entirely about accumulating singles and then stealing second base. Baseball Savant has his expected wOBA, based on his exit velocity and launch angles, at just .269, ranking 219th of 241 batters with at least 200 at-bats. His speed will get him some extra hits that xwOBA won’t give him credit for, but he’s regressed as a hitter this year, even with his lower strikeout rate.

So if Nunez is pressed into regular duty, there’s at least a chance that the Red Sox could find themselves with another weak bat who also isn’t much in the field. And that’s probably why the team is hoping he doesn’t take Devers job; he’s likely just around in case the 20-year-old can’t handle the big leagues quite yet, and to give the team a better platoon option so Devers doesn’t have to get exposed to elite left-handers too early.

His positional flexibility makes him a solid bench player, but the weak bat means that if he’s not playing third, it’s tough to imagine him playing regularly. It’s hard to imagine him taking much playing time from Andrew Benintendi in left, especially if he’s mostly playing third against LHPs. He can spell Dustin Pedroia at second base occasionally, but Pedroia’s going to play most of the games at the position as long as he’s healthy. Ideally, the team would have acquired a third baseman who could displace Mitch Moreland at first base if Devers held the 3B job, but there’s really no reason to play Nunez at first, where both his bat and glove would be inferior to Moreland. And if you DH a guy who hits the ball like Nunez hits the ball, while playing Hanley Ramirez at first base, you’ve really made some poor roster choices to end up there.

So Nunez fits best as a part-time player in Boston, and offers some depth in case Devers ends up overmatched this early in his career. In an ideal world, his postseason role would be that of the team’s dedicated pinch-runner and contact-bat off the bench when the team just needs a single. In a more realistic scenario, he’ll share third base with Devers and give Pedroia some days off at second base while maybe playing some outfield once in a while too. If he ends up as the team’s everyday third baseman, that’s the worst outcome, but at least they’d still have someone better than they had in the first four months of the year.

To land a couple of months of a decent role player, the team gave up their third round pick from the 2016 draft and a live-arm that is so far from the Majors that he could feasibly have a future big league match-up against someone who has not yet been born. Here’s what Eric Longenhagen had to say about Anderson this spring.

Rare is the relief prospect with a five-pitch mix, but Anderson is that, with a low-90s fastball that will touch 94 and a enough secondary pitches to form a J-pop group. He works an upper-80s cutter under the hands of left-handed hitters, has a low-80s slider with more loop that he runs away from righties, and he can turn over a fringey upper-70s curveball, too. He also has a rarely used changeup. Anderson was the closer at Florida and it’s worth considering whether he might fit in a rotation and was just pushed to the Gators’ ‘pen simply because they have so much other talent on the roster.

As Eric notes, Anderson has a starters’ repertoire and has worked exclusively in the rotation as a professional, putting up not-horrible numbers in his career so far. But as a college guy who isn’t really missing bats or getting ground balls in A-ball, this isn’t a guy the Red Sox needed to hang onto at all costs. Any time you trade an arm, there’s always a chance he’ll add five ticks to his fastball and learn a new pitch while turning into an ace, but Anderson’s chances of pitching in Boston any time soon don’t look great, and his upside seems somewhat limited at the moment.

So Boston gave up a couple of fringe prospects for a moderately-useful role player who they probably hope doesn’t have to play everyday. It’s a reasonable enough acquisition for a team headed towards the postseason. Nunez does more to raise the Red Sox floor than their ceiling, but there’s value in a stop-loss who ensures that a total lack of production at one spot will keep you from playing in October. And if their new insurance policy happens to steal an important base or two in the postseason, then that could justify giving up a couple of arms you might not miss that much on its own.