JonM and I were talking about that via IM. Reynolds was saying since it was a passed ball, the hitter has to either be tagged or thrown out at first. The logic is that since he has to try to advance to first, the runners have to be moving and there is a force out available at all bases. So if that was true, Barrett could have stepped on home and thrown to third for a DP. However, the rule is that you cant advance to first on a K if there is a runner on first. So basically the play was dead when Burrell K'd and runners could advance at their own risk.