In the century that football has grown into the nation’s most-watched sport, the N.F.L. has expected players to act like warriors willing to suck up the pain and sacrifice their bodies for the good of the team, and to be grateful they are paid handsomely to do it.

Yet even as awareness of the physical toll of the sport rises, the sudden retirement just two weeks before the start of the season by the Colts’ quarterback Andrew Luck at age 29 still provided a jolt.

Luck, a former first overall draft pick and one of the league’s brightest stars over the last seven seasons, said Saturday he could no longer take the years of pain and rehabilitation from a host of cringe-worthy injuries: a lacerated kidney, injured ribs, at least one concussion, torn cartilage in his throwing shoulder and, most recently, a calf and ankle injury.

It was not the first time a young player had stepped away supposedly in the prime of his or her career — several have done so in recent years — but it was one of the more vivid examples of the changing dynamics of a league striving to portray the game as safer than ever while its players increasingly weigh the consequences of continuing a career where the long-term physical issues only build as the seasons pile up.