From what the TV guys said last night, in the 9th when Billy was on 2nd and Choo on 1st after the ill-fated sac bunt by BP, he was basically on 3rd by the time the ball crossed the plate. He had to go back to 2nd and tag but he was stealing then.
Good article from Baseball Prospectus about Billy's night.
http://www.baseballprospectus.com/ar...rticleid=21845