Instant replay is a fairly recent addition to NFL football. Instant replay is great, because important games should not turn on mistakes or non calls by the officials. It does, however, have some problems.
When it started out, the officials had 30 seconds to review the play, and issue a ruling. That system was removed, because rushing the official did not accomplish the goal of getting the call right. In the current system coaches have 2 challenge flags they can throw. Throwing a flag triggers a review of the play.
The problem is, these flags are being abused. It is possible to throw a flag on a unchallengeable call. Pass interference, for example, cannot be challenged. If the coach throws the flag and finds out he cannot challenge the call, the flag is returned.
So what happens is the coach basically gets a free conference with the official while everyone picks around. Coach throws the flag, finds out he can't challenge, and gets his flag back.
Jacksonville's coach Jack DelRio took it a step further. He just help up the flag and got a conference with the zebras while his team was on defense. What this does is slow down the game, lets his defense get a breather, and throws the opposing offense off balance. (DelRio is not the only coach to do this, just the most recent.)
Football is not Shakespeare, there should be no long, drawn out "to challenge or not to challenge". Play should continue, and if a coach wants to challenge, he should throw the flag. Can't challenge it? Lose the flag. Mis-throw? Lose the flag. You get two a game, use them wisely.
Take the game out of the officials hands, and let them play football.