I was just recently (5 minutes ago) watching an American football game. It was a quite important 4th down play to win the game, and the play was challenged. The cameras had absolutely ZERO view of the ball; however, the ruling on the field was a catch. So, with NO view of the ball whatsoever, the referee's call overturned the ruling on the field. Wouldn't this just be 'The ruling on the field stands'? Can the referee who called the completion come back and say it wasn't a catch and he called it wrong on the field?
Basically, what goes into calling a play back from a challenge/official review besides what the cameras see?