After news broke that Mariano Rivera had destroyed his ACL, there were two things to talk about: (1) what it would mean for Mariano Rivera, and (2) what it would mean for the New York Yankees. Not only did one have to wonder about the rest of Rivera's career; one had to wonder how much damage the injury would deal to the Yankees' overall true-talent. How many wins would the Yankees lose by losing Mariano Rivera for five months? (of the regular season)
If you're familiar with the Wins Above Replacement statistic, you'd know that it says Rivera is worth about 2-3 wins above replacement each season. So that would be an estimate of Rivera's value. But ex-pitcher C.J. Nitkowski is active in Internet circles, and he's pretty well versed on cutting-edge statistics, and he doesn't think that value estimate is high enough. An excerpt from Nitkowski's blog post:
Here is what I think was so badly missed. The trickledown effect on the loss of Mariano Rivera is unquantifiable. I know you in the community hate that word, just like you hate "team chemistry", "gutsy player" and "intangibles." The reality is that you cannot say with any certainty how many games this injury will cost the Yankees, but I can say it will be more than 2.
That does not mean David Robertson himself will cost the Yankees 2 more wins than Mariano would have. It means you've lost a Hall of Fame arm in your bullpen. Robertson moves up, Soriano moves up, Boone Logan moves up, Corey Wade moves up, etc.
Your middle relief is now weaker, your setup corps has changed, or can't pitch as much in middle relief because someone has to take on Robertson's and Soriano's innings, which were so valuable.
That's just one chunk of it, and you should read the whole thing. Nitkowski concludes:
This is just one example of how it works, there are a million other scenarios. Robertson vs. Rivera, sure there is some loss but maybe not as much as the casual fan thinks. Losing Rivera is a bigger blow to the bullpen as a whole, both mentally (sorry, it's true) and physically.
From the statistical perspective, we get something of a counter from the inimitable Tangotiger:
So, it’s not a question of how good Mo is. He’s #1, and with a bullet. The question is how much value can such a player have in the role that’s available to him. And my answer is 2.5-3 wins a year.
And that also happens to be the official position of the Yankees and Rivera himself, since he’s being paid at 15 million dollars a year, and wins are going for 5 to 6 million dollars each. And 15/5 and 15/6 gives us 2.5-3 wins a year.
Tangotiger has reached out to Nitkowski, trying to see if they can have a discussion. If the do end up having a discussion, it'll presumably be public, and if they have a public discussion, we'll write about it here. Reliever value is one area where a lot of people disagree, so when you're dealing with a reliever like Mariano Rivera - only the greatest reliever in the history of the game - you're going to get a wide variety of opinions on what a major injury's going to mean.