For much of the season, Adam Warren has been one of the more reliable starting pitchers for the Yankees. Yet, with the return of Ivan Nova, the team found itself with six healthy starters, and eventually this lead to Warren being moved into the bullpen. As Jason pointed out here, this was the only option the Yankees really had, and yet it hasn't been particularly popular. Mostly because of the perception that Warren was demoted to accommodate a struggling CC Sabathia.
We don't know how much of a role Sabathia's contract played in the decision making there. It is worth noting that the Yankees have been heavily rumored to be in pursuit of a trade for a rotation upgrade, and that the team is giving CC the fifth starter treatment of skipping a start, where the off days ahead of the All-Star break have lined up to make this a reasonable possibility. This suggests the Yankees aren't convinced that keeping Sabathia in the rotation for the rest of 2015 is necessarily the best way to go, and yet he remains a starting pitcher for now while Warren is in the bullpen. It may seem curious decision making until we note Brian Cashman's comments on the matter; Warren was sent into relief mostly to manage his innings.
Hardly surprising. Warren's 87 innings to this point are a career high for him in the majors, about 10 more than he threw in both 2013 and 2014. He did come through the minors as a starter, but he's a full three years removed from that type of workload. The Yankees were never likely to let him get up to 150 innings or so, double what he threw last year. He's had 16 starts to this point, in all likelihood he'd have been given another eight, maybe 10 at absolute most. If the Yankees had pulled Sabathia out of the rotation and kept Warren, they'd have to swap the two back by late-August, if not before, this time likely shutting down Warren for the year. Of all possible outcomes, the one that features getting nothing from Warren down the stretch and potentially in the postseason seems the least promising. The Yankees simply couldn't leave themselves one rotation injury from relying on Chris Capuano to see them through critical September starts.
Instead, Warren has been sent to the bullpen. He has made two relief appearances so far, pitching a combined 4.1 innings. It appears Joe Girardi is using him as a long man, as opposed to a single inning right-handed reliever. This will helpfully leave Warren at least somewhat stretched out, able to slide back into the rotation when needed in-case of injury. In the meantime, though, it isn't as though being a long reliever means he will serve in a mop-up role. Capuano remains on the roster to pitch through a blowout. Rather, Warren might be trusted to go multiple innings for games still in the balance. Going off the early results - of course a sample size of two relief outings - Girardi has indeed deployed Warren in games that are still winnable. First, 2.2 innings in relief of Nova against the Angels, in a one-run game; the second, 1.2 innings in extras against Tampa Bay where he was brought in ahead of Chasen Shreve and Bryan Mitchell.
It is possible that the Yankees will at some point decide they have seen enough from Sabathia in the rotation, at least for the rest of 2015, and bite the bullet on a starting pitcher trade that sends Sabathia into a mop-up role and potentially Capuano off the roster entirely. If that happens, it may seem like the Yankees gave up prospects to acquire a rotation upgrade when they already had one in-house. However, this team has proven committed to closely monitoring the workloads of their pitchers, and there was never any likelihood of Warren pitching 30+ starts in his first full year in the rotation. Even if Warren will be limited to pitching fewer innings in the second half of the season, he can continue to be deployed in higher-leverage situations. In this way, as long as he continues his successful 2015, he could continue to have a significant positive impact on the Yankees win-loss record.
All things being equal, of course a starting pitcher will have more impact than a middle reliever, but in this case Warren will likely be most valuable to the Yankees as a relief arm that pitches key situations for the rest of the season. Hopefully, the rest of the season includes October baseball.