The key to whatever the Red Sox can accomplish in October isn't Nathan Eovaldi. It isn't Rafael Devers. Nor is it Xander Bogaerts, Hunter Renfroe, Chris Sale, or J.D. Martinez.
The key to the postseason is a Euro-stepping second baseman with a flair for the dramatic who is nonetheless injury-prone and largely unproven eight years after being selected in the first round of the 2013 MLB Draft. He has appeared in just three games since July 18, hasn't recorded a hit in more than two months, and in case you haven't noticed those 6:30p sunsets, he's running out of time.
His name is Christian Arroyo, and the Red Sox soon will need him more than ever.
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Stack their roster like a Jenga tower and Arroyo is a lonely middle piece upon which multiple layers rest. Whereas the Red Sox feature more players than spots between first base, designated hitter, and left field, they're painfully thin at second base, especially since September pickup Jose Iglesias is ineligible for the postseason by virtue of not being in the organization on Aug. 31.
If Arroyo plays, the Red Sox defense makes sense. If he doesn't, then prepare to watch that tower fall.
Arroyo returned to the roster on Tuesday after more than three weeks on the COVID-19 injured list. That IL stint came on the heels of a month-long absence after he strained a groin stretching for a throw during his debut at first base.
Manager Alex Cora noted that COVID hit Arroyo particularly hard, which would be an issue on its own. But making matters worse, it extended his layoff to basically two full months, meaning only 10 games remain to regain feel before the most important contests of his life.
"We just have to make sure that Christian's timing is on point because when he comes here, I'm not saying he's going to play every day or whatever, but at one point we know what's going to happen and he's going to be very important to what we're trying to accomplish," Cora said. "We need him to be -- and I'll repeat myself -- on point timing-wise."
If there's one facet of the game that will keep the Red Sox from advancing in the playoffs, it's defense. And the Red Sox desperately need Arroyo at second because the alternative wreaks havoc on the rest of the alignment.
If Arroyo can't play second, then unless Cora wants Jonathan Arauz and his .185 average on the roster, he'll probably have to put Kiké Hernández there. That wouldn't normally be a problem -- after all, the Red Sox signed Hernández to play second -- but Hernández has emerged as one of the best defensive center fielders in baseball, a point he reiterated on Tuesday by throwing out Mets first baseman Pete Alonso at home in a 6-3 victory.
"He's been great the whole season," Cora said. " Actually, today we got the ballot for the Gold Glove. You look at the numbers and all that. You're like, you know what? I don't want to say it cost him a Gold Glove because he signed here to play second base, right? But he's been really good (in center). His routes, his decisions, he's stopped the running game. For me, it's very important to keep him there."
When Hernández plays center, the rest of the defense fits. Left fielder Alex Verdugo and right fielder Hunter Renfroe grade as above-average on their respective corners, but when Hernández plays second, Verdugo shifts to center, where he's subpar, and either Martinez or Kyle Schwarber downgrades left field.
Hernández, meanwhile, has cost the team four runs at second (vs. a plus-11 in center) according to Baseball Info Solutions. With the left side of the infield already a defensive question mark, and with first baseman Bobby Dalbec still ranking among the worst at his position (though his glove recently has improved along with his bat), that's too much bad defense at too many positions for the Red Sox to make a realistic run.
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Arroyo, on the other hand, has been good for four runs saved in 49 games at second, where he's sure-handed and dependable. If he can return with enough time to regain that form, the Red Sox could resemble the best version of themselves from May and June.
If he can't, their defense will suffer, perhaps fatally. That makes a player we've barely seen in two months the unlikely key to the playoffs.