Those of you who are sabermatrically-inclined probably just responded with a collective eye-roll. Wins Above Replacement ranked Rivera as only the 5th most valuable pitcher on the Yankees last season, behind CC Sabathia, A.J. Burnett, Andy Pettitte and Phil Hughes. When you include position players, Rivera drops to 15th, just behind Brett Gardner.
How is that possible? Dave Cameron explains:
While the quality of [relievers] work is very high, the quantity is low, which limits their total value. It’s nearly impossible to rack up huge win values while facing less than 300 batters per season. Yes, each of those batters faced are more critical to a win than a regular batter faced, but this is accounted for in WAR.
It's not to say that WAR is a perfect measure - I don't think anyone believes that Brett Gardner is more irreplaceable/valuable than Rivera - but if the numbers are even close, then it's clear that people (media, fans, etc.) tend to overvalue relievers. When you look at these numbers, it becomes clear that some front offices share this skewed view and are willing to overpay them as well.
Why is that? Perhaps a series like the one the Yanks just wrapped up can shed some light.
None of the six pitchers Joe Girardi and Terry Francona called upon to start the last three at Fenway games factored into a decision. Only Sabathia and Lackey were particularly close - both of them watching their lead evaporate under the watch of the man who relieved them. Therefore, each contest was decided by pitchers who entered the game via the bullpen.
Chan Ho Park was on both sides of that equation, taking the loss on Sunday night after allowing a two run homer to Dustin Pedroia and getting the win last night after throwing three scoreless innings while the game was knotted at 1. Jonathan Papelbon had a similar experience, converting a save on Friday and blowing one last night. Each played the role of goat and hero just a few nights apart.
While WAR can objectively weight the contributions of pitchers by leverage, we as fans can't hope to be nearly as unbiased. As a close game progresses, stress and anxiety in the attentive viewer build. Our joy and frustration are multiplied by those factors and relief pitchers are the one major variable in the equation. The lineups are essentially the same but as the stakes within the game increase, the faces on the mound change.
And that's why someone would try to make the case that Mariano Rivera is the most important player on the Yankees. He might not be the most important from a zero sum sabermetric perspective, but he is on a purely observational standpoint, if you have a rooting interest in the team, Mo is the man. CC Sabathia throws far more innings, but they don't seem to have as much on the line. Mark Teixiera plays in almost every game, but most of his contributions occur under ordinary circumstances.
When Rivera enters the game, as a fan, you can exhale. We've seen him do it so many times before, it's hard not to be confident. You trust that he's going to get the job does until he doesn't - and then you assume that he'll do it next time. Conversely, the three innings that Chan Ho park pitched felt significantly more tense and uncertain. The difference between them is in that respect more than commensurate with their respective abilities.
Of course, Mo did what he usually does during the past two nights. He gave up just one baserunner and the go-ahead run never came to the plate. A couple of late nights at the office and two saves in the book.
It might not show up in advanced stats or translate to as many wins above replacement as we would assume, but Rivera and other trustworthy relievers contribute greatly to the enjoyment of rooting for the team. If you spend enough time reading about and understanding the principles of sabermertics, you should realize that his importance is magnified in your mind. But when a save situation rolls around, he really does seems like the most important guy on the team.