THIRD STRING PLUCKING

The PeeDee’s Tony Grossi thinks the rule about third quarterbacks is “dumb.”
However, his summary of the rule lacks context. He wrote:
If a third quarterback is inserted before the fourth quarter, a team’s first two quarterbacks cannot be used in the game at any position. It is a coach’s decision as to whether a third quarterback will be used. The active quarterbacks do not have to be injured for a team to use its third quarterback.
The big picture is that teams have 53-man rosters, but only 45 players, plus a third quarterback, can dress on game day. This mitigates the effect of injuries. If there were no exception for the third QB, he would very often be designated inactive, since the odds on needing him are long. The provision actually prevents the farcical and potentially dangerous scenario of two QBs hurt and a trained backup stuck in street clothes.
If a team wants to deploy three quarterbacks without restriction, it may activate them as part of the 45-player allotment.