Coaches can criticize because they're not on the field but they have to be careful doing it. Coaches will talk in generalities as in, "We didn't make plays downfield" but won't name any names, for example. Teammates criticizing others is dangerous because TBH, no one plays a perfect game. Until that happens any player that does criticize should say nothing because at some point they probably screwed up in a game. Players play & coaches coach.