Joakim Soria and the Value of a Postseason Relief Ace

The Tigers, as they seemingly always do, have a bullpen problem. They rank 26th in the majors in bullpen ERA (4.37) and 25th in FIP (3.92), as Joe Nathan has been a disaster in the ninth inning, and Al Albuquerque, Phil Coke, and Ian Krol haven’t been very good at protecting leads before Nathan takes the hill either. When your most reliable reliever is Joba Chamberlain, you know there’s some issues.

So on Wednesday night, the Tigers did what contending teams with bullpen issues do; they paid through the nose — giving up Double-A starter Jake Thomspon and rookie reliever Corey Knebel — to get an experienced, high-quality closer, acquiring Joakim Soria from the Rangers. Soria has been fantastic this year, posting a ridiculous 1.07 FIP, thanks to the lowest walk and highest strikeout rate in his career. Oh, and the fact that he hasn’t allowed a home run yet. That helps too.

Of course, not allowing home runs in Texas is a neat trick that Joe Nathan pulled off last year, and that hasn’t really carried over to his pitching this year in Detroit, but even when the home runs return, Soria should still be pretty big upgrade for the Tigers relief corps. However, even very good relievers only pitch about 10 innings per month, and with just a little over two months left in the season, there just aren’t that many innings left for Soria to make a significant difference in the standings. Besides, the Tigers were extremely likely to win their division even without Soria, as they currently hold a 6 1/2 game lead over the Indians and a 7 game lead over the Royals.

In terms of moving the playoff odds needle, perhaps no significant trade made this month will have less of an effect that the Tigers acquiring Soria. But this trade isn’t about the regular season. This trade is about the postseason, and the potential impact Soria could have in October.

We’re all pretty familiar with the fact that relievers just don’t pitch enough innings to be highly valuable in the regular season, but the game is played differently in the postseason. The increased frequency of off days makes it easier to lean on your best relievers more often, and the importance of each game provides an incentive to make sure that the best pitchers are on the mound the most often. And this shows up in their usage patterns.

For illustration, the most frequently used relievers throw about 5% of a team’s total innings over the course of the regular season; that’s ~75 innings out of around 1,450. Most are a bit under that, but if you’re really aggressive with your closer usage or have a relief ace working in a setup role, you can give him 5% of the total innings pie from April through September.

Now, let’s take a look at the percentage of innings pitched by elite relievers in last year’s postseason. Eight of the top 20 relievers in 2013 WAR made it to at least the division series and pitched in multiple games. Here are their percentages of innings pitched for last postseason:

Player	IP	Team IP	%/IP
Koji Uehara	13.2	142.1	9.6%
Sean Doolittle	4.1	44.0	9.3%
Trevor Rosenthal	11.2	152.0	7.7%
Mark Melancon	3.2	52.0	6.2%
Jason Grilli	3.1	52.0	6.0%
Joaquin Benoit	5.2	96.0	5.4%
Kenley Jansen	4.1	90.1	4.5%
Drew Smyly	3.0	96.0	3.1%

After throwing 5.1% of the Red Sox innings in the regular season, Uehara threw nearly double that amount in the playoffs. For reference, 9.6% of a team’s total regular season innings would equal out to about 140 innings per year. Based on the fact that the average leverage index when Uehara entered the game was 1.76, you could equate the impact of the innings he threw in the postseason to a starting pitcher that threw 246 innings in the regular season.

Yeah, elite relievers can matter an awful lot in October, which is why teams continually trade legitimate prospects to acquire them in July. Of course, Uehara carried the heaviest workload of the elite relievers, so this is basically the absolute best case usage scenario for a relief ace in October. The A’s managed to use Doolittle similarly, but only through one round, and every other team who advanced beyond the division series gave a lighter workload to their best bullpen arms. The average percentage of innings pitched for these eight relievers was 6.5%, which still translates a regular season workload of about 95 innings, but doesn’t match what Boston got out of their closer.

But, again, we have to factor in that while these pitchers are throwing fewer innings, they are pitching in innings that have a greater impact on wins and losses than a starting pitcher does, and we can’t simply equate one reliever inning with one starting pitcher inning. The way this is handled in reliever WAR is through chaining, which gives the reliever credit for pitching in higher leverage situations but doesn’t incorrectly assume that those innings would have gone to a replacement level reliever instead.

So, yes, Soria might only throw a handful of postseason innings, and reliever performance is volatile enough that perhaps he won’t end up making a significant difference for the Tigers. In that case, they’ll have just punted one of their best pitching prospects and a power arm who might have been a useful reliever himself. Certainly, this is the kind of deal that could easily backfire, and the Tigers may very well regret this deal in the long run.

But they made this because of the potential for an Uehara-style impact. Uehara’s dominance over a very large workload was one of the primary reasons the Red Sox won the World Series last year, and despite their diminished importance in the regular season, relievers can matter an awful lot in the postseason. We shouldn’t diminish Soria’s potential impact on the Tigers playoff run just because individual relievers don’t matter as much in the regular season.

If Brad Ausmus learns from the mistakes Jim Leyland made last postseason — note the very low percentage numbers for Benoit and Smyly on that list above — and aggressively uses Soria this October, this trade could end up being a significant difference maker for the Tigers. The idea that relievers don’t really matter that much holds up to scrutiny in the regular season, but the postseason is a different game, and it’s one where guys like Joakim Soria can matter a lot more.