Indeed there are
MM only put JP in the 4th quarter, because if JP was put in before then, the bills could not put Mathews or Bledsoe on the field. In other words, the third stringer is not allowed to play in the first three quarters unless the the first two QB's were knocked out of the game. upon the third stringers entrance into the game before the fourth quarter, the First and second stringers are unable to play for the rest of the game.