If you have to review a video frame by frame to see if a call is correct, then it's not a bad call. It might be incorrect, but it's a justifiable call if it's that close. Exception: if it's a non-contact violation (such as a travel) and you need that degree of granularity to show that the violation actually happened, then it's a pussy call. There is just no way that a player (who is, of course, also attempting to play ultimate besides being a ref) in real time can discern this.
That is all.