The ball fluttered in the air and all but one of the 22 players on the Three Rivers Stadium turf on that cold December day 50 years ago essentially stopped.

Franco Harris never did.

The Pittsburgh Steelers running back kept right on going, the instincts that carried him through his life both on and off the field during his Hall of Fame career taking over, shifting the perception of a moribund franchise and a reeling region in the process.

The Steelers rarely won before his arrival in 1972. The moment his shoe-top grab eternally known as the “Immaculate Reception” entered the lexicon, they rarely lost.

Mr. Harris, whose heads-up thinking authored the most iconic play in NFL history, has died. He was 72. Mr. Harris’ son, Dok, told The Associated Press on Wednesday that his father died overnight. No cause of death was given.

His death comes two days before the 50th anniversary of the play that provided the jolt that helped transform the Steelers from also-rans into the NFL’s elite, and three days before Pittsburgh is scheduled to retire his No. 32 during a ceremony at halftime of its game against the Las Vegas Raiders. Mr. Harris had been busy in the run-up to the celebration, doing media interviews Monday to talk about a moment to which he is forever linked.

“It is difficult to find the appropriate words to describe Franco Harris’ impact on the Pittsburgh Steelers, his teammates, the City of Pittsburgh and Steelers Nation,” team President Art Rooney II said in a statement. “From his rookie season, which included the Immaculate Reception, through the next 50 years, Franco brought joy to people on and off the field. He never stopped giving back in so many ways. He touched so many, and he was loved by so many.”

Even in retirement, Mr. Harris remained a fixture in the community and a team whose standard of excellence began with a young kid from NewJersey who saw the ball in the air and kept on running. It wasn’t uncommon for Mr. Harris to stop by the Steelers’ practice facility to chat with players who weren’t even born before his fateful play.

“I just admire and love the man,” Coach Mike Tomlin said. “There’s so much to be learned from him in terms of how he conducted himself, how he embraced the responsibilities of being Franco for Steeler Nation, for this community ... He embraced it all and did it with such grace and class and patience and time for people.”

Mr. Harris ran for 12,120 yards and won four Super Bowl rings with the Steelers in the 1970s, a dynasty that began in earnest when Mr. Harris decided to keep running during a last-second heave by Pittsburgh quarterback Terry Bradshaw in a playoff game against Oakland in 1972.

With Pittsburgh trailing 7-6 and facing fourth-and-10 from its own 40-yard line and 22 seconds remaining in the fourth quarter, Mr. Bradshaw drifted back and threw deep to running back Frenchy Fuqua. Mr. Fuqua and Oakland defensive back Jack Tatum collided, sending the ball careening back toward midfield in the direction of Mr. Harris. Game officials weren’t sure who deflected the pass; replays were inconclusive.

While nearly everyone else on the field stopped, Mr. Harris kept his legs churning, snatching the ball just inches above the turf near the Oakland 45, then outracing several stunned Raider defenders to give the Steelers their first playoff victory some four decades after founder Art Rooney Sr. brought the still-fledgling NFL to western Pennsylvania.

“That play really represents our teams of the ’70s,” Mr. Harris said after the “Immaculate Reception” was voted the greatest play in the league’s first 100 years in 2020.

While the Steelers fell the next week to Miami in the AFC championship, Pittsburgh was on its way to becoming the dominant team of the 1970s, twice winning back-to-back Super Bowls, first after the 1974 and 1975 seasons and again after the 1978 and 1979 seasons.