Tomase: Which Red Sox starter will be odd man out when Sale returns?

File this one under the heading of: Good Problems to Have.

File it further under: Issues that May Resolve Themselves.

But for now, it's a question without an obvious answer: If the Red Sox rotation stays healthy and effective, who gets bumped to the bullpen when ace left-hander Chris Sale returns from Tommy John surgery in the second half?

Before the season, "throw a dart" would've been an acceptable response, because expectations were low. We knew the rotation would improve upon the unwatchable mess of 2020, but clearing that bar didn't exactly require a Fosbury flop.

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More than two months into this season, however, there's no obvious candidate to kick to the bullpen. Based purely on results, it would be Eduardo Rodriguez. Based on stuff, it would be Martin Perez. Based on service time, it would be Nick Pivetta. Based on repertoire, it would be Garrett Richards. It's hard to envision any scenario in which it's a healthy Nathan Eovaldi.

So who is it?

First, some numbers. Outside of two starts from Tanner Houck, the aforementioned quintet has started every game. Eovaldi and Pivetta lead the staff with 3.78 ERAs, while Richards and Perez trail slightly at 3.88. E-Rod brings up the rear at 5.59.

FIP tells a different story. Eovaldi is the runaway leader at 2.40, with everyone else grouped between 3.40 (Pivetta) and 3.89 (Richards). Despite his up-and-down start, E-Rod actually checks in at 3.70, the victim of some very soft -- albeit consistent -- contact.

The top four starters have each thrown between 60 and 67 innings, with Rodriguez just a tick behind at 58. All five of average just over five innings a turn.

The club's 4.17 ERA ranks 14th in baseball and seventh in the American League, basically middle of the pack. In that sense, the idea of making room for Sale isn't so much that the Red Sox feature five aces, but that the four arms beyond Eovaldi feel indistinguishable.

The issue won't require resolution for a while. Manager Alex Cora on Tuesday likened Sale's recent bullpen to what a pitcher would throw in January after arriving in Fort Myers. That puts his return somewhere in August, a point that pitching coach Dave Bush reinforced when he told The Athletic that Sale's looking at a timetable of roughly two months.

A lot can happen between now and then to make the decision easy. After a run of four straight wins, for instance, Perez was shellacked by the Astros on Tuesday, allowing six runs in two innings. His lifetime numbers suggest little more than a serviceable, average big-leaguer. He's the club's fifth starter for a reason.

And yet . . . until Houston teed off, Perez owned the best ERA on the staff (3.05), as well as encouraging quality-of-contact numbers dating to last year. While it's tempting to call him crafty, it's also worth noting his sinker has topped 96 mph. He's not easily barreled up.

And even though he has only made 19 relief appearances in 10 years, he'd be a logical candidate to send to the 'pen, since American League contenders like the White Sox, Astros, and Athletics pound left-handed pitching, and swapping Sale for another southpaw makes logical sense alongside Rodriguez.

So that settles it. It's Perez, right? Not so fast. Another way to look at this is need. If Perez joins the bullpen, he'd likely slot as a long reliever. The Red Sox are still trying to find a reliable bridge to closer Matt Barnes. Lefties Darwinzon Hernandez and Josh Taylor and righty Adam Ottavino are currently in that mix, though each struggles with walks.

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If the eighth inning remains a hole in August, then a case could be made for shifting Pivetta or Richards, a pair of power right-handers with late-inning stuff. Pivetta, in particular, seems to have the kind of mentality that would lend itself to the seventh or eighth.

Neither has been particularly good in the first inning, however, and eighth-inning relievers aren't afforded the luxury of settling into a groove. Richards is allowing a staff-worst 1.029 OPS in his first inning of work, with Pivetta right behind him at .883.

The wild card in all of this is Rodriguez. He just posted a 7.28 ERA in May that is not sustainable, though bad luck certainly played a part as all manner of bloops and bleeders found holes. Still, he's not missing bats, and he has allowed more home runs (nine) than anyone on the staff. He has been fighting it all season, and if any member of a relatively brittle staff eventually requires an IL stint, he'd be a reasonable nominee.

The good news is this shouldn't be a serious topic of discussion until after the trade deadline, at which point Chaim Bloom will have presumably addressed multiple flaws.

While Bloom has consistently noted that Sale represents a potentially more impactful deadline addition than anyone he could acquire externally, it's also worth noting the trickle-down effect Sale's arrival could have on the relief corps, because as things stand now, an effective starting pitcher will be joining their ranks.