During a play where B5 hits a ground ball, what must the base umpire do if he reverses his call after confirming with the plate umpire?

When the base umpire reverses his call after confirming with the plate umpire, it indicates that the initial call regarding B5's status needs to be corrected based on the newly gathered information. In this scenario, if the base umpire determines that B5 is indeed safe and this is in opposition to the earlier call, then the proper course of action is to address the implications for R2, the player on second base.

Allowing R2 to score while calling B5 out would create confusion regarding the sequence of events and the ruling on B5. Similarly, not addressing R2's position while changing the call would not accurately reflect the play as it unfolded. By calling R2 back to second base, the umpire ensures that the game is correctly officiated according to the rules and the flow of the play is appropriately restored. This approach maintains the integrity of the game and aligns with the regulations governing the situation.