Personal foul?

[stegenref]

Last night I was working HL in a JV game. There was a sweep to the other side and just as the play was ending, I saw some trash on the backside...a kid from the defense grabbed an offensive player from behind by the shoulder pads and tried to throw him to the ground. I threw a flag and ran out to tell my WH about it. I told him I had a personal foul and told him what happened. He asked me if it happened after the play and I kind of hesitated, because it was so close to the end of the play I wasn't sure if it happened before the whistle was blown or not. He asked me if I wanted to call it a dead ball foul, so I said yes.

Question #1: What difference does it make if it happened before or after the whistle. I assume it has something to do with penalty enforcement on a live ball foul versus a dead ball foul?

Question #2: Did I correctly report it as a personal foul or should I have called it an unsportsmanlike conduct penalty, or is an USC penalty just a type of personal foul? I realize I may just be worrying about semantics here, but I want to get it right.