In a sense, Carlos Beltran’s awful season is Alex Rodriguez’s fault. Over the past three years – really, about two years of playing time due to injuries - Beltran has +3.9 oWAR and -4.2 dWAR. That’s league-average hitting and the worst outfielding since Raul Ibanez, who’s a not bad comp: both still hit at a similarly advanced age but suffered a Sampson-like loss of all defensive ability when they lost their hair prematurely. What you naturally do with Beltran’s skill set is DH him – except that spot is justifiably taken by A-Rod, who's a better hitter, older, and even less able to play the field because his (former) position is more demanding.
If he must RF rather than DH, Beltran likely deserves the bench. He’s sub-replacement level, and sinking: -0.2 WAR in 2014; -0.5 WAR in just half of 2015, a roughly -1 WAR/yr pace. Slade Heathcott and Mason Williams, if they ever walk again, are so vastly superior defensively that even with a poor bat they can reach replacement level -- enough to exceed Beltran); until then, Ramon Flores’s .800 OPS in AAA makes it hard to see him running a -1 WAR/yr pace like Beltran’s. Like CC Sabathia, Beltran has crossed Dante’s “abandon hope all ye who enter” sign: Beltran’s and Sabathia’s performances have been bad, and declining, for so long, and at a sufficiently advanced age, that there’s no realistic hope of improvement; at -2 to -2.5 dWAR/yr, Beltran needs to hit like an MVP to be close to league-average, and he hasn’t been that hitter since 2008. I’m not exaggerating in saying that if for the entire the season the Yankees suffer through CC in the rotation (over Warren) and Beltran in RF (over whatever Scrantonite is available), that will have cost the team 4-5 wins, and maybe a playoff spot.
A full benching won’t happen, but I’d take the half-a-loaf option of cutting Beltran's to half-time, give or take – by platooning him not by opposing starting pitcher, but by Yankee starting pitcher, because some starters are far more likely to yield the liners and flies Beltran lets drop. I don’t have data on which part of the outfield each pitcher’s contact goes to, but we do know how many line drives, fly balls, and home runs each pitcher gives up. Home runs, of course, aren’t typically catchable by anyone, but home run rate is a decent proxy for rate of giving up liners and fly balls that are long or hard-hit – the sort a bad outfielder wouldn’t get, but a good outfielder might.
Here are the current Yankee starters (plus Warren, who’s likely in some way to get more starts this season) by handedness (which I know you already knew), line-drive %, fly ball %, combined liner plus fly %, and HR rate (per 9 innings). For present purposes – avoiding outfield contact Beltran would handle badly – you probably get the super-secret color code: red=bad, green=good, and yellow=middling.
Reasonable minds could disagree on what these numbers mean, and what (if anything) they mean for Beltran, but the color-coding shows what I’d do: bench Beltran for starts by Sabathia, Warren, and Tanaka.
• Pineda and Eovaldi, though very different pitchers this year, are the gold standard for making outfield defense less relevant: they give up few flies, liners, and home runs – so, fewer tough plays for a weak outfielder like Beltran.
• Nova is almost as good as Pineda and Eovaldi at making outfield defense irrelevant, but his much higher home run rate hints that more of his flies and liners are hard-hit or long – the sort of outfield contact that an outfielder with range might grab, but Beltran won’t.
• Tanaka, though having a strong season, gives up a tick more flies and liners than Pineda, Eovaldi and Nova, but also gives up many more home runs – again, hinting at more hard-hit outfield contact that puts a premium on outfield defense. This surprised me, because Tanaka lives so consistently low in the zone that I'd guessed he’s a ground-ball machine – but he’s not, whether because his mistakes get hit hard, because he’s so predictably always low in the zone that many hitters adjust, or for some other reason.
• Sabathia has been strong against the lefties more likely to hit to right field, and probably sees fewer lefties as a result – but he gives up tons of outfield contact, including very hard-hit outfield contact, as the astronomical home run rate indicates. He’s basically the last guy you want backed up by an outfielder as bad as Beltran.
• Warren, though I think he really should still be in the rotation, needs stronger outfield defense than Beltran can provide: his liner-plus-fly rate is almost as high as Sabathia’s; and while the low HR rate shows he doesn't give up as many long flies and liners as Sabathia, he's a righty, so compared to Sabathia, he faces more lefties who tend to send their outfield contact to RF.
So if the Yankees aren’t going to turn Beltran into a once-weekly DH and pinch-hitter, as many of us would like, then it would be nice if they at least limit him to, say, half-time outfield play – not only because his middling hitting and horrible defense don’t warrant full-time play, but also because, at his age, he’ll probably be a stronger player all around with regular rest. And if you’re going to bench Beltran a third or half the time, why not do it for the pitchers who launch a lot of contact, and hard-hit contact, into the outfield? So I’d bench Beltran during starts by Sabathia, Warren, and Tanaka. I don’t lay great odds that Girardi will do this, but I wish he would.