I would guess the advanced stat at b-r.com that correlates best to Running rating is XBT% (Extra Bases Taken). The percent of times the runner takes more than one base on a single or more than two bases on a double per opportunities to do so.


timz is right that the percent of times the runner takes an extra base isn't useful for measuring baserunning unless you also look at outs.

Imagine two players who, during the course of the season, have identical opportunities to go from 1st to 3rd on singles with 0 outs. One player takes the extra base 48% of the time, and the other player takes the extra base only 16% as often. So the first player--whether by superior speed, more agressiveness, greater desire to win, ignoring the 3rd base coach, it doesn't matter--advances the extra base 3 times as often as the second player. Does that mean he is a better baserunner? What if the first player also is thrown out at 3rd on 4 times as many attempts as the second player? Assuming they each have 50 opportunities, it would look like this:

Player A: Take extra base 24 times, thrown out 8 times, hold 18 times
Player B: Take extra base 8 times, thrown out 2 times, hold 40 times

According to the table of expected run value of base-out situations derived from Retrosheet information that can be found here: http://baseballanalysts.com/archives/2006/07/empirical_analy_1.php , Player B's baserunning in these situations has essentially had a neutral effect on his team, turning 75.20 expected runs into 75.27 expected runs, for all practical purposes break-even. But Player A's more agressive but more risky baserunning has actually cost his team runs, turning the same 75.20 expected runs into only 73.44 runs. Not a big loss, by any means, but still not much to show for all that messin' about on the basepaths. The reason is that each time he successfully takes the extra base on those singles, he increases his team's expected runs by only about 1/4 of a run, but every time he's thrown out he lowers his team's expected runs by almost a full run, 0.982 runs to be exact. Therefore, unless he's successful more than 4 times for every time he's thrown out, he's hurting the team with his baserunning. The goal of baserunning, after all, is to increase the chances of scoring runs, not to demonstrate speed.

It should be stressed that the table I used for the above example measures the average runs expected, not the chances of scoring at least one run, which is different. There could very well be situations where it is more important to increase the odds of scoring at least 1 run even if it decreases the chance for a big inning and thereby reduces the average runs expected, and that could change the break-even point on success rate.