We’re going to be doing a lot more with Dan Fox’s baserunning numbers across a number of platforms. You’ll see his baserunning numbers in Baseball Prospectus 2008, and we hope to turn them into a continually updated stat report for next season.
They’re also going to make their way into PECOTA, so one of the questions that I’ve needed to address is as follows: is baserunning a skill? This actually entails a couple of sub-questions:
1. Is baserunning strongly correlated from year to year?
2. If so, is the driving force simply a player’s speed, or is there a separate, measurable baserunning skill apart from speed?
The answer to the first question is a strong “yes”. Without considering runs generated from stolen bases, the correlation in EqBR (Equivalent Baserunning Runs) from year to year is on the order of .50-.55, depending on how you slice the data. That correlation might not seem that high, but considering that players only have a certain number of opportunities to show off their baserunning skills in any given year — they have to reach base, among other things — it’s as much a persistent ability as something like fielding.
As for the second question, the answer is also “yes”, although speed is the primary factor, with what we might call baserunning judgment being a secondary factor. The graph that follows compares the BP/PECOTA version of Speed Score (for these purposes, we’ve removed the component of Speed Score based on runs scored, which is directly dependent on baserunning) to a “rate” version of EqBR (specifically, EqBR per 200 times reaching base, excluding home runs).
This graph considers all players who reached base at least 100 times in 2007 (again, excluding home runs); the correlation between EqBR and Speed Score for these players was .56. There are a few average players with average speed who are excellent baserunners, and a few slow players who are average baserunners, and so forth. But the long and short of it is that baserunning results are mostly dictated by speed. There aren’t any genuinely slow runners who are great to have on the basepaths, for instance.
A regression analysis does find that there is some manifestly statistically significant component to baserunning above and beyond speed. But if you assume that a fast runner is an effective baserunner, and a slow baserunner an ineffective one, you’re going to be right upwards of 80-90% of the time.
The last question, of course, is how much baserunning really matters. And the general rule of thumb is that it can make about a win’s worth of difference at the extremes: a really fast/skilled baserunner will produce about 8-10 extra runs for his team on a going-forward basis as compared with a really slow/terrible baserunner. Or, if you prefer, a great baserunner will produce about an extra half-win for his team (4-5 runs) per season versus an average baserunner.
This is nothing to sneeze at. Baserunning is another in that category of things that might be overrated by the mainstream media, but has nevertheless been underrated by sabermetricians.