Weighted On Base Average
From Wiki
Weighted On Base Average (wOBA) is a measure of offensive productivity created by Tangotiger. It is designed to have a scale similar to that of On-Base Percentage. The event coefficients are based on the linear weight values of each event minus the linear weight value of an out, which are then increased by 15% to achieve the scale parity with OBP.
wOBA = (.72*(W - IW) + .75*HB + .90*S + .92*ROE + 1.24*D + 1.56*T + 1.95*HR)/PA
Here is a version that also includes SB and CS:
wOBA = (.72*NIBB + .75*HBP + .9*S + .92*ROE + 1.24*D + 1.56*T + 1.95*HR + .25*SB - .5*CS)/PA
wOBA can then be converted to runs above average per plate appearance as follows:
(wOBA - Lg(wOBA))/1.15
