There are those who think relief pitching is fungible, but that's not accurate. The role of closing might be overrated in its overall importance to the game, because it's the last thing that happens before a W is officially added to the standings, but there are great pitchers with that job who shut down the opposition night after night.
Mariano Rivera is the greatest of those closers, and even today, 17 years after he logged his first save, he's still flat-out ridiculous. Rivera might have been 41 years old in 2011, but it was one of his finest campaigns. The 2012 season started out much the same, with eight strikeouts in eight innings, and a 2.16 ERA earned in the course of five saves.
The Yankees mourned his loss on Thursday night, but with 137 games left on the schedule and yet another tough AL East road in front of them, their next step is to figure out what a bullpen without Mariano Rivera looks like. To the Yankees' credit, their bullpen already involved far more than just Rivera, as they also have set-up men David Robertson and Rafael Soriano, the latter of whom was signed before 2011 for three years and $35 million with Rivera's potential retirement in mind.
It's an enviable position, even after the loss of Rivera. Robertson has been dominant since becoming a full-time reliever with the Yankees in 2010, posting a 199 ERA+ over his last 139 innings pitched, powered by 12.6 strikeouts per nine. He walks his share of hitters, but whiffs nearly three times as many batters as that, and he has little trouble keeping the ball in the yard. He's also been able to shut down both lefties and righties in his career, a must for both a setup man and a closer.
Soriano has been less consistent, due to injuries over the years, but when he's healthy he's hard to hit. Since 2009, his first full season back from elbow surgery, Soriano owns a 150 ERA+, nearly 10 strikeouts per nine, and a 3.1 strikeout-to-walk ratio. He spent significant time on the disabled list in 2011, and if that happens again, combined with Rivera's absence, New York's bullpen starts to look much thinner.
For now, with everyone except Rivera assembled, this is still a strong unit. The loss of Rivera will have a ripple effect, though. The Yankees will be down to one reliable setup man when one of Robertson or Soriano is promoted to the closer role, and more innings -- including high-leverage ones -- will go to arms that, while capable, don't match up with the trio New York started the year with.
Boone Logan has been great at shutting down left-handers over the years, but Logan's career OPS allowed against right-handers is 877, and while he had a reverse split in 2011, that's unlikely to hold up over time. The Yankees have limited him to about 40 innings per season because of his splits, so more of him would go against his optimal usage plan.
Cory Wade has been very effective for the Yankees in the short time he's been with them, posting a 1.90 ERA and 4.5 K/BB. But he's also bounced from team to team in his career, and while some of those pitchers turn out to be Mike Adams, that's a rare, best-case scenario. He's useful, but again, the risks are higher when Wade is pitching in a high-leverage spot than they would be with Soriano or Robertson.
David Phelps might turn out to be an intriguing bullpen arm, but, at the moment, he's in the rotation now that Freddy Garcia has been demoted. When Andy Pettitte returns, either Phelps or Phil Hughes will end up back in the bullpen. While Hughes has struggled as a starter, switching to relief full-time where he needs fewer effective pitches and can let loose with his velocity should make him an effective piece in a role where New York needs him.
The Yankees are lucky that they don't need to make a mad scramble for replacements, even with the greatest (and still great) closer in history is out for the season. But they're a weaker team Friday morning than they were 24 hours before, and as the Rays and Red Sox can both attest, a few injuries are all it takes to derail you in the powerful AL East.
Then again, this is the Yankees, and if they need a short-term reliever to help make up for it, they will find and acquire him. Mike Gonzalez is still a free agent, and while he might not be the most effective replacement against righties, he's still more than capable of retiring his fellow lefties. New York wants to be under the luxury tax within the next season or two, but in 2012, that's already a lost cause: if they have to acquire a free-agent-to-be closer who becomes available, like say, Francisco Rodriguez and what's left of his $8 million, they likely will. They also have a number of pitching prospects in the upper levels who can be shifted to the bullpen in the short-term if necessary.
Losing Rivera will most definitely affect the Yankees bullpen. But New York isn't without on-hand options, and they have the resources to find new ones, both internally and externally.