With no outs and a runner on third base (R3), the batter (B1) grounds to the shortstop. The shortstop throws to 1st base to easily retire B1. When the shortstop throws over to 1st base, R3 runs for home. After the first baseman retires B1 at 1st base, the first baseman throws home in an attempt to retire R3 at home.

 

However, the first baseman's throw is low and hits B1's bat -- which had been dropped completely in fair territory as B1 ran to first base. The throw ricochets off the bat and R3 is easy safe at home.

 

What does the umpire do now?