Plummer says he wants to play handball into his 70s. So in April, he began an 18-month hiatus to have surgery to repair his hips, injured from drop-stepping for a decade in the N.F.L. While sidelined, however, he realized he still missed football.

“Like my wife told me, ‘There’s opportunities and you never do them, but start living your life, start doing this stuff,’ ” Plummer said. “ ‘One day, you’re going to be dead and gone and not have these opportunities anymore. Or you’re going to be so far gone from the game and such an old has-been that they’re not going to want to have you around.’ ”

His mind drifted back to Colorado, where his wife had family. Their return was clinched when he spotted a house for sale within 10 minutes of the most pristine outdoor handball courts in the state.

A few weeks after the move, Plummer attended the Broncos’ season opener against the Steelers by himself, with a ticket given to him by the Broncos’ owner, Pat Bowlen. When parachutists descended into the stadium for a pregame celebration, Plummer saw that the crowd was distracted. He left the owner’s box, walked down to the mezzanine and stood inside a walkway at the 45-yard line.

Plummer said fans did double-takes when they saw him. But as the game continued, he reminisced with longtime security guards, talked with a young fan whose parents had told him not to bother Plummer, high-fived a mascot and was treated to a few beers by fans who said they remembered him fondly.

Plummer later slipped down to the sideline to watch Manning and Roethlisberger, who had each ruined his postseason hopes. But Plummer did not dwell on that. He cheered on the Broncos’ defense, the way he used to as a player, when he wanted to get back out onto the field as quickly as possible.

After the Broncos won, 31-19, Plummer sat on a patch of grass outside and watched jubilant fans exit the stadium.