Calls in tennis tend not to be subjective so VAR is easy. Cricket less so but there are still a lot of straightforward decisions. Football is a lot trickier particularly relating to handball where the interpretation seems to change week by week.
As for fouls, we still have too many instances of fouls in the box not being awarded with commentators and pundits saying "that would be a foul anywhere else on the pitch", a distinction not made anywhere in the laws of the game.
I accept these microphone jockeys are rarely qualified refs, but I think we've all seen and thought the same thing when watching games.