Andrew Luck has long been exceptional.

As an athlete. As a student. As a person with more perspective than many in the game of football.

At Stanford, he returned for his senior year to finish his degree and play one more year with the Cardinal, pushing back against the groundswell of opinion that he was crazy because he was guaranteed to be one of the NFL’s top draft picks in 2011.

So it’s not a complete surprise that Luck is the most recent NFL player to say “enough.” To value a quality of life going forward. To put a stop to the endless cycle of pain and injury.

Yet, some people can’t understand that very personal and difficult decision. The reaction to Luck’s Saturday night announcement that he was retiring from the Indianapolis Colts, at age 29, was fast and ferocious. It provided some disturbing insight into our society.

And it should be very disturbing news for the NFL. The pain of this game is real.

The way the story unfolded was a tutorial on the modern news cycle. The news broke on ESPN while Luck was on the sideline at Lucas Oil Stadium for a preseason game. Fans saw it on their phones and booed the man who had laid down his body for seven years for their team.

By the time Luck got to the podium for his news conference, the internet was awash in hot takes. Luck was too soft, too “millennial” to do the hard work of rehabilitation, lacking in commitment. He was lashed with anger from bettors, fantasy-football team owners and the media.

That was a scary view of the ugliness of football, of the sick underbelly of a game in which intolerance and lack of empathy too often seem to be the currency of fans. Where players aren’t treated as actual human beings but some kind of property. Maybe this dehumanization is a side effect of fantasy football, where regular people think they “own” a player. Maybe it’s the result of the unceasing violence of the sport: If we really thought these were actual humans colliding into each other at top speed, it would be hard to process.

The most valuable lesson I’ve ever had in the game of football has come from standing on the sideline during games. The cliche is 100 percent true: It is like witnessing a high-speed car crash. But with human beings. Who get up and do it over and over and over again. It is absolutely terrifying.

Luck is a human being. A man with a brain and a body.

Since his arrival in the NFL in 2012 (as the top draft pick despite his return his senior year, a vindication of trusting his instincts), that body and brain have taken a beating.

After dazzling the league in his first three years, Luck has — beginning in 2015 — suffered:

A sprained shoulder. A lacerated kidney that caused him to urinate blood. A torn abdominal muscle. Torn cartilage in two ribs. A torn labrum in his throwing shoulder. At least one concussion.

He missed all of 2017, after shoulder surgery. He was the Comeback Player of the Year last season, leading the Colts to the second round of the playoffs.

But then he suffered another injury — this time to his calf and ankle — in the offseason. In his retirement news conference, he said he was in constant pain.

“For the last four years, I have been in a cycle of injury, pain, rehab,” Luck said. “It’s been unceasing and unrelenting. I felt stuck in it.

“It’s taken my joy of this game away.”

For some, that’s not good enough. They feel like they own Luck, like he owes them further sacrifice.

Other NFL players mounted the fiercest defense of Luck.

“How dare Luck not sacrifice his body for MY entertainment,” his former Stanford teammate and former Seattle Seahawks receiver, Doug Baldwin, wrote sarcastically on Twitter. “Who cares if your shoulder is too messed up to pick up your child. Who cares if your knees are too messed up to play with your kids. Who cares about the quality of YOUR life, what about the quality of MY Sundays?”

Kids might be in the back of Luck’s mind. He and his wife Nicole, a former Stanford gymnast, announced in June that they were expecting their first child. That changes a person’s perspective on what is important and what the future is going to look like.

Another Stanford teammate, 49ers cornerback Richard Sherman, tweeted: “This is a very rough game. Most people who have not played at this level will never understand what we put our bodies through season after season. We don’t need the sympathy because this is what we signed up for but to ‘boo’ a man that battled for that city is disgraceful.”

Luck said he heard the boos.

“It hurt,” he said.

Everything has hurt. For too long. “I feel tired and not just in the physical sense,” he said.

His retirement comes as owners are pushing to extend the regular season to 18 games. As the NFL celebrates its 100th anniversary season while ignoring many of the past’s greats who are suffering and don’t have decent benefits. As attitudes about injury and football change. As youth football participation numbers decline.

“You’re seeing more players prioritize their health over money,” former 49ers linebacker Chris Borland, who retired after one season, told the New York Times.

Luck has long been exceptional. He’s stepping away with his integrity, his brain. And that Stanford degree.

Ann Killion is a San Francisco Chronicle columnist. Email: akillion@sfchronicle.com Twitter: @annkillion