receiver might have stepped out of bounds look for a bare head. If you happen to see one and weren’t looking for it, someone stepped out and you missed it.

If it’s a close play at the goal line, it’s not a TD till they put their hands up.

If a flag goes up at the snap and they’d don’t stop the play, it was probably offside. If they do whistle it dead, it was probably illegal procedure (false start).

Learn the hand signs for penalties and distant referees will use these to communicate with the head referee initially and you’ll know what’s being called.