Butch Dill/Associated Press
The start of the N.F.L. season was a rough one for some of the league’s most bankable quarterbacks. Andrew Luck retired before the start of the season. Drew Brees hurt his thumb and will be out another month or so. Ben Roethlisberger is done for the season because of an elbow injury. Eli Manning, the cornerstone of the Giants since 2003, was replaced by a rookie, Daniel Jones.
But as the N.F.L. rolled through its fourth week, the league’s quarterback corps by necessity or design has gotten younger in a hurry — with mixed, and sometimes exciting, results.