What would really be valuable would be a stat that somehow gave credit for stranding inherited runners, but cost a reliever when he got the team into a jam.
Turns out, there's a stat for that. It's called Adjusted Runs Prevented, or ARP.
I've become hesitant to introduce any new stats, because this is when the vast majority of eyes glaze over. I'm going to try it anyway with ARP, because it's just so darn simple. It's also ultimately very, very powerful when talking about relievers. But first, the simple:
ARP = expected runs when a reliever enters a game - expected runs when he left the game.
So say a reliever comes in with runners on the corners and no outs. From studying tens of thousands of previous MLB innings, we know, on average, how many runs will score that inning. It's about 1.9. So if the reliever strands those runners, he gets +1.9 ARP. If he gets out of the inning with just one run scoring, he gets +.9. If two runs score, he gave up more runs then the average, so his ARP is -.1.
Or say a reliever comes in to pitch the ninth inning. The average runs scored in an inning are .56. So if he pitches a perfect ninth, he gets +.56 ARP. And if he gives up a 2-run home run to Alex Rodriguez (for example) his ARP would be -1.44.
If you have some more questions about ARP, leave them in the comments section. We can do some more complicated examples there if you like.
Anyway, ARP is exactly what it is named; it is how many runs a reliever prevented. And those runs aren't random - they're the average runs from decades of major league games. Finally, there is no goofy extra credit for pitching late innings - really valuable middle relievers or setup men often lead the league in ARP. It is an EXCELLENT statistic for showing which relievers have had the best year. It's a MVP stat for relievers.
So who were the top relievers this year? Of the 729 relievers tracked by Baseball Prospectus, here's the top five:
Andrew Bailey (OAK) +29
Michael Wurtz (OAK) +28.3
Joe Nathan (MIN) +28
Matt Guerrier (MIN) +26.8
Mariano Rivera (NYY) +25.8
That third name might surprise some Twins fans. Turns out Joe Nathan had a hell of a year. Remember, he lost ARP runs in those games where he collapsed, but overall he was extremely effective. You can't find three guys in the majors that were more effective than him.
What's more, this was not a one-year thing. Nathan ranked #7 in overall ARP last year. By the way, there was only one other guy who was in the top 10 both years. It's Mariano Rivera.
But it's also not just a two-year thing. Because in 2007 Nathan was #8. Rivera finished 21st that year. And it keeps going...
In 2006, Nathan was #6 and Rivera was #8
In 2005, Nathan was #15 and Rivera was #2.
In 2004, Nathan was #8 and Rivera was #6.
As you go through this list, year by year, there are two names that are on the list over and over - Nathan and Rivera. Those two, and ONLY those two, have been the model of consistency, effectiveness and health since Nathan joined the Twins in 2004.
Now, this doesn't mean that Nathan can't be traded. For the right package of players, just about nobody on the Twins should be untouchable.
But to say that Nathan is slipping, or nearly finished, is almost indefensible. His handful of failures have been more memorable because of when they happened and who they happened against, but objectively they barely dent the successes he had.
However, there is something that is even more indefensible, and that is to say that he can be easily replaced. Or even replaced at all:
- Matt Guerrier? Great this year. But his ARP last year was negative.
- Jose Mijares? His ARP was 12.8, less than half of Nathan's.
- Pat Neshek? Um, you might want to look at Francisco Liriano this year before you commit to someone coming off of Tommy John surgery?
- And the most popular - someone else? After all, Nathan wasn't anything special when we got him...
Wrong again. Nathan was already on that list of ARP leaders back when he was throwing middle relief for the Giants, ranking 24th out of 676 relievers in 2003. He was just two slots below Francisco Rodriguez that year, and that was when KRod was exploding onto the scene.
The doubters can bitch about the stat, but they're going to need bring something tangible to the table besides a couple of bad nights. The dreamers can can talk about a trade, but they're going to need to bring some realistic player packages. And both of them are going to need to bring a replacement for someone who is arguably the second best relief pitcher of this decade.
And that includes 2009.
Late addition: For those of you saying we should trade Nathan for "the right package", I really would like to hear what you consider the right package to be in the comments section. Give me teams and names that you think are realistic and would improve the team. Thanks!