The “B Position – Runner on First Base” Mechanic is a drop-step movement used by the Base Umpire when there is only a runner on first base and a ball is batted fair to the infield, setting up the possibility of a double play. The drop-step movement from the Hands-On-Knees set position allows the umpire to clearly see the catch of the ball and touch of the base by the defense, as well as the runner approaching the base. With the secondary drop-step, the umpire is able to clearly see the play develop at first base.
With only a runner on first base, and a ball is batted fair to the outfield, the Base Umpire moves from the B Position into the infield and pivots to clearly see the play being made in the outfield, runners touching the bases, as well as any subsequent play(s) that may made on the runner(s) at second or first base.
If you have not watched the “The Hands-On-Knees Set” and “A Position – The Pivot” mechanic videos, you may want to do so prior to watching this video. At the completion of this video, you should be able to be in proper position and properly execute B Position mechanics according to Little League Standards.