With no outs and no base runners, the batter (B1) walks and then hustles down to first base. B1 touches first base, runs through (and past) the base, turns into foul territory, and makes no attempt to advance to second base. The ball is thrown to the first baseman -- who then tags B1 while B1 is walking directly back to first base (still beyond first base and still in foul territory).

 

The defensive team thinks that B1 should be called out. The offensive team thinks that B1 is protected back into first base (as is often the case with a batter-runner advancing to first base). What does the umpire do now?