Call it or not??

[frank22]

Last night in Junior High game, A1 controls rebound and stands still waiting for everyone else to clear out. B2 comes around the backside of A1 and slaps the arm instead of the ball. Close game and getting more physical as time went on, I called foul. I noticed the coach's face on the way down the court and he didn't look happy about the call. He did not say anything though. Should I have let it go?