- advancing an extra base on a hit (i.e. going from first to third on a single, second to home on a single or first to home on a double)
- advancing on a ground out
- advancing on an air out
- stealing a base
- advancing on a wild pitch, passed ball or balk
- running into an out on a hit, ground out or air out
- getting picked off or caught stealing
- otherwise running into an out on the bases
Similar calculations are done for other events (ground outs, air outs, other base running) with points subtracted for outs on the bases. At the end, everything is summed to get bases gained above average (BGAA). The full algorithm can be found here.
The American League BGAA leaders in 2009 are shown in Table 1. You can see that recently acquired Johnny Damon finished seventh in the league at 18.9 bases above average.
Table1: American League BGAA Leaders, 2009
Ellsbury, Bos......... 34.9
Getz, Chi............... 27.0
Kinsler, Tex........... 24.4
Bartlett, TB........... 22.6
Davis, Oak............ 21.7
Punto, Min........... 20.4
Damon, NYA....... 18.9
Andrus, Tex.......... 18.2
Bautista, Tor........ 18.0
Gardner, NYA..... 17.9
Some information used in this figure was obtained free of charge from and is copyrighted by Retrosheet. Interested parties may contact Retrosheet at 20 Sunset Rd., Newark, DE 19711.
This system does come with a caveat. In the BGAA system, every type of base advancement is treated the same. In reality, base advancement is more likely in some situations than others. Specifically, the probability of advancement on hits, ground outs and air outs changes according to the numbers of outs and the location of batted balls. The equivalent base running runs (EqBRR) statistic at BaseballProspectus.com does take those things into consideration.
Damon had an EqBRR of 2.9 runs above average. He ranked lower on the EqBRR system - 21st in the league - than he did on the BGAA system. Still, he finished higher than any Tiger on either system. The leading Tigers baserunner in 2009 was Adam Everett - 10.3 BGAA and 2.1 EqBRR.