if the 3rd qb is put in the game, the 1st and 2nd can't come in again?

[OverAndBack]

Game day roster sizes have fluctuated over the years. Since 1991, NFL teams have been allowed to dress 45 +1, with the 46th guy being the (emergency) third quarterback. The only reason you get the extra guy is if he's an emergency quarterback so you can use your 45 (the old limit) on guys who will actually play.

The reason there are restrictions about that player's use is to keep you from stashing another player and effectively dressing 46. Teams were only dressing two quarterbacks for strategic purposes because you rarely needed three. If you're going to put that player into the game prior to the 4th quarter, the cost of doing so is necessarily pretty stiff - you can't bring back either of the two guys who are supposedly healthy who are in front of him.

It used to be that if the 3rd QB entered the game at any time, the 1st and 2nd were barred from returning to the game. Now you can put the 3rd guy in in the 4th quarter with no loss of the right to use #1 or #2. And the first two guys don't have to be injured for him to go in. It's a coach's decision.