I don’t think that Jim Leyland intended to use Ryan Perry in the most critical situations of the season, but that’s how it turned out.
Baseball statistics websites such as FanGraphs and Baseball-Reference keep track of a metric called Leverage Index (LI). This statistic quantifies the importance of a situation in a single number. If you want to do some heavy reading on the subject, check out this, this, and this.
Basically, the leverage index is the potential change in win expectancy of a particular situation. An average situation is defined as having an LI of one, a high leverage situation might be ‘ahead by one entering the bottom of the ninth’ (3.6), and a low leverage situation might be ‘down by four entering the bottom of the sixth (0.2). Here’s a chart of LI by situation.
The goal is to save your closer for the situations in which you can leverage their abilities the most, and to burn your “inning eaters” (Eddie Bonine, Brad Thomas) in low leverage situations. Here’s how the Tigers’ relief pitchers were used according to Leverage Index (click on the image for a larger version):
These numbers are actually the average situation into which each pitcher was called into the game (sorted by number of relief appearances).
Ideally, your top reliever would be used, on average, in situations with a leverage index near 2.0. None of the Detroit relievers were close to that, but Perry was the closest at 1.49. This isn’t really what we want to see. Perry is a pretty good reliever (or at least I still expect him to become one), but he wasn’t the Tigers’ top guy. He was asked to get the team out of situations that were stickier than those that Jose Valverde and Phil Coke came into.
I know Valverde had some struggles in the second half of the year, but he got the job done far more often than not. He’s the guy making the big bucks, and he’s the guy that needs to be in there getting the tough outs.
On the other end of the spectrum, Eddie Bonine, Brad Thomas, Fu-Te Ni, and Enrique Gonzalez were all called upon in situations that were below average on the leverage index scale. This is exactly what we want to see as fans. These aren’t the guys that should be relied upon to get critical outs, and by and large, they weren’t asked to.
It’s also interesting to note that Robbie Weinhardt was used in some pretty critical spots. He struggled in his first big-league action, but he wasn’t floundering in mop up time. This was some big-time action so maybe we shouldn’t be too hard on him.
I’d have to go back and check the number of high leverage situations that the Tigers faced in the late innings, but it appears to me that the back end of the bullpen may have been mismanaged. In the future, if you’re wondering whether or not a manager is using his relievers correctly or not, leverage index is a good stat to start with.