## Friday, August 25, 2006

### Advancing on outs -- how many runs is a skilled baserunner worth?

In a three-part series on Baseball Prospectus (subscription may be required, but he blogs on his study here), Dan Fox looks at which baserunners benefit their teams most by advancing on outs.

To do that, he starts with the usual base-out run value charts. For instance, suppose there’s a runner on second and nobody out, and the following batter hits a ground ball to the first baseman. If the runner advances, there will be a runner on third and one out, which is worth an expectation of 0.978 runs scoring in the remainder of the inning. If the runner stays put, the value is 0.704 runs. So that particular advancement would be worth 0.274 runs, which would be credited to the baserunner.

Fox compiled full baserunning stats for the 2000-2005 seasons, based on play by play data. The
first article in the series deals with ground outs; that article contains an explanation of the system, but, because of an error, the results were adjusted in part 3.

It turns out that the best ground-ball baserunners in that six-year period were Juan Pierre, who created 9.37 ground ball baserunning runs above what the average runner would do (EqGAR), and Adam Kennedy, who had 9.05. The third through tenth-place runners were between 5.31 and 3.82 runs.

The
second part of the study dealt with fly balls. Derek Jeter was the best fly-ball advancer with 6.93 extra runs (EqAAR). Ray Durham was second with an EqAAR of 4.49, and the next eight were 4.15 down to 3.25.

Aside from the identities of the best and worst players – for which you can see full top-ten listings in the study – an imporant question is just how much a good baserunner can contribute to a team. A naive estimate would be simply the number of runs saved, such as 9.37 for Juan Pierre. However, as Fox notes,

"… the extreme values … don’t represent an actual skill, but instead a combination of skill and random variation which has the effect of pushing some values to the extremes."

That is, the study makes it appear that the best baserunners can save their teams between 4 and 9 runs. But we can’t say that’s true – those might have just been the luckiest players. At the other extreme, it’s possible that skill doesn't matter at all -- that all players are equally good baserunners, and Pierre and Jeter wound up at the top simply because they happened to be on base for a lot of slow grounders and deep fly balls.

That’s unlikely, of course. But just as the effect of skill is unlikely to be zero, it’s also unlikely to be as high as the 4 to 9 runs observed. The truth is somewhere in the middle. It is probably closer to the top than to zero, as suggested by the fact that Juan Pierre is a very fast runner, the type we would expect to be leading the chart.

But to know for sure, to find out the actual value of baserunning skill, more work is required. If Dan pubishes full data, we could do a check using Tangotiger’s technique.

At Monday, August 28, 2006 9:50:00 AM,  Tangotiger said...

I recommend Tippett's article as well:

http://www.diamond-mind.com/articles/ichiro.htm

It's also pretty plain to see that speed is limited in impact. The gap between the top and the bottom is about .333 bases advanced (i.e., if a bad runner makes it .167 times, a great runner makes it .500 times).

Since each base is roughly worth .25 runs, each time a runner is on base, and followed by an event that speed plays a role, we are talking about .08 runs each time.

How often will that happen? A runner will be on first or second say 200 times a teammate is at bat, and that teammate will get a hit or out that can be leveraged, what 25% of the time? So, 50 times his speed comes into play. Times .08 runs gives you 4 runs, or +/- 2 runs.

You can probably work out better numbers than my off-the-cuff ones (and I have in the past... I seem to remember getting +/- 4 or 5 runs).

The key though is that this question is easily guesstimated using "baseball guts".