What makes Mo so great

In the wake of yet another brilliant postseason performance, Dave Allen looks at Mariano Rivera's pitches and goes a fair piece toward explaining just what makes Mo so great:

    Rivera is a great pitcher, so we should not be surprised when he has an amazing run of 16 innings. But that does not mean that he can will himself to pitch 16 one-run innings whenever he chooses. So in this post, when I look back at his amazing performance, I don’t want it to sound like I think this was inevitable and there was no way he could have given up any runs. Rather, I am just looking back and seeing how it happened.


    Again you see the bimodal distribution of pitches either along the inside edge or outside edge. Against RHBs he mixes in his fastball. Batters swung at it more often than his cutter and made contact at a good rate, but they were fouls or outs. With the cutter he got lots of whiffs up-and-in, called strikes down-and-in, and got more swings and contact, again mostly outs or foul balls, away.

    Anyway that you look at it, another sixteen incredible innings in the career of the best relief pitcher ever.

That's my new favorite baseball term: bimodal distribution. It means that most of Rivera's pitches cross one edge of the plate or the other, and it is perhaps the best explanation for Rivera's success.

Maybe his postseason numbers are merely a subset that fits nicely within the larger set of Rivera's career numbers. Maybe he doesn't have some special ability to thrive on the biggest stage. Two points about that, though:

  1. He has pitched better in the postseason, which has to count for something.

  2. There's actually some evidence that he does pitch differently when the chips are really down.

First, the performance: Rivera's career ERA in the regular season is 2.25, which of course is brilliant. But his postseason ERA -- and we're talking about 133 innings -- is 0.74. And that's not just an ERA fluke. While Rivera always does everything well, he does almost everything better in the postseason. Rivera's strikeout rate actually is lower in the postseason, but he more than makes up for that with a lower walk rate.

But it's the home runs that really tell the tale. In his regular-season career, Rivera has given up 0.5 home runs per nine innings, which, depending on where you set the innings cutoff, might be viewed as the all-time record. In the postseason, though? Rivera has allowed 0.14 home runs per nine innings -- two home runs in 133 innings. There's some luck there, of course. On the other hand, Rivera has done all of that against good (or great) teams, the vast majority of them with good (or great) lineups.

As if his rate stats weren't enough, all those two-inning postseason stints further separate him from his peers.

One thing I've never seen: a measure of postseason value. We can look at how many wins a player adds, based on performance and "leverage"; that is, the state of the game when the player does what he does. Protecting a one-run lead for two innings is obviously more valuable than protecting a three-run lead for one innings, and we know how to measure that value. But I think it would be useful to incorporate that analysis within the larger context of postseason series. It's one thing to say that Rivera has been worth 5.3 postseason wins in his career, but wouldn't you rather know how many championships he's been worth?

Anyway, if you want to take a shot at that, feel free (and you're welcome). Not that Rivera's reputation needs any help.