Or even banned from the league if someone isn't smart about it. The time to do it is on a Brady interception or a defensive fumble return, but I am guessing he has eyes behind his head. There isn't many interceptions or fumbles so there will be limited opportunities

Also, back in the older days, players stayed with the same teams for long periods and built up rivalries and hatred. Nowdays, players change teams so often that many players are friends with players on the other teams because they might have been teammates just last season.