Wednesday, June 25, 2008

Optimal Baserunning
I've seen a few stories lately on how the Red Sox are stealing a lot of bases at a high success rate this season. So far, led by Ellsbury, they're stealing at a pretty amazing 84% rate. Considering the breakeven point for hurting your team in the runs department is around 65% (this is the percent the defense is trying to keep the running team below), that looks pretty good. But I was wondering what is an optimal number for a team success rate? I can't seem to find this information anywhere, so I'm going to make it up. Let's assume there is a flat distribution of stolen base opportunities, ie the same amount of situations where a baserunner will be safe 0% of the time, 25% of the time, 50%, 100% and all points in between. The distribution is probably normal around the break even point in real life but flat is much easier to work with. Runners on base should be trying to go any time a steal gives their team an edge so they should be running in all situations where the anticipated success rate is >=65%. If the distribution of opportunities is flat, then a team which runs the bases perfectly will on average steal successfully (.35/2)+.65=83% of the time.

I can't say whether the goal this season was to steal around 85% or whether it's just because the Red Sox suddenly have some guys who can run but are still relatively conservative (compared to other teams), but to me it looks like right now the Red Sox are taking the optimal advantage of the opposing teams' defenses. In a league where most other teams are stealing at the equilibrium rate where the net value added is 0 (in other words trying to steal as often below the breakeven point as above it), the Red Sox result looks like a pretty huge edge. It will be interesting to see if A. other teams start copying their optimally conservative/aggressive approach and/or B. if opposing defenses ever adjust to the fact that the Red Sox have been robbing them blind.