rimming???

[first2third]

First off just the phrase rimming doesn't sound like anyone, especially umpires should be involved in such activity. However, here is the sit.

Working 3-man championship 16U accelerated, R1 on 1st. I am PU, rabbit rotated to B, 1BU at A. Fly to center rabbit goes out a little late but not to bad. I yell 2 man. 1BU goes behind runner in foul territory ball is caught on a dive R1 tags and there is a banger at second. Guess who has the call??? I decide I do as I went to a holding position near the mound and am the closest to the play. Thank god I am still semi young and quick, I get there in good position and there are no complaints at all as the runner just beats the tag. Two innings latter the 1BU apologizes and claims he was using the college rim technique. I do some JC and I think then shouldn't you be on the outside in front of the runner on the rim towards second base not in foul territory? Am I wrong? Do I not understand rimming? Help me out here. Always learning but never coming to a full knowledge of the truth.