Third QB rule comes into focus

The Patriots designating rookie Julian Edelman as their third quarterback Monday night has raised some questions as to what exactly that means. Here are the key points:

1) A third quarterback is a 46th player on the 45-man gameday roster. The rule is designed to help teams not be caught short at the game's most important position in the event of multiple injuries.

2) The third quarterback can enter the game at any time, but if he enters before the fourth quarter, the first and second quarterbacks are eliminated from the game.

3) Edelman is not restricted to playing quarterback if he enters the game. This may be a case where Edelman's forearm injury is serious enough that he can't play for an extended period, but could contribute a play or two in crunch time.