Forget the booing, which was merely an unfortunate soundtrack and not representative, from all appearances, of the status Andrew Luck holds in the hearts of the city of Indianapolis.

Luck announced his retirement from pro football last week at age 29, and he was escorted off the field at Lucas Oil Stadium by a scorned gaggle of football fans wondering: What in the world just happened?

Because everywhere else where such things are noted and notable, that was the same exact reaction when the news became public.

What in the world just happened?

We look at pro athletes as the very core of our dreamscape, because what could be better than that: They are forever young, forever strong, forever wealthy, forever powerful, forever basking in public adulation. There’s a reason why most rock stars fantasize about being athletes: because it’s hard to think of anything better in life.

“Rock star or star football player?” Rod Stewart asked in 1975, around the time he was becoming one of the most bankable names in the music business. “I don’t think that’s even a fair debate, mate.”

So when they walk away before they are pushed — or when death, illness or permanent injury makes it something beyond their own choice — there are certain stages to the reaction:

1. Holy [smokes]!!

2. Is he holding out for more money?

3. Give it time. He’ll be back.

4. He’s really not coming back, is he?

5. Good for him/her.

Jim Brown has long been the gold-standard for that, of course. Like Luck, Brown played his last snap of professional football at the age of 29, rushing for 12 carries and 50 yards (and catching three balls for 44 yards) in 23-12 loss to the Packers in the NFL Championship game at Lambeau Field.

Six months later, delays on the set of the film “The Dirty Dozen” meant Brown would have to miss a part of training camp. This didn’t sit well with Browns owner Art Modell, who threatened to fine Brown $1,500 for every week he missed. That didn’t sit well with Brown, who announced his retirement instead.

Brown wasn’t just the greatest running back the sport had seen to that point (and may still be, depending on who you talk to); he was indestructible. He was carved out of marble, impossible to tackle, impossible to contain, impossible to injure. If anyone could play football forever, it was Brown.

But he walked away. And never came back.

Neither did Barry Sanders, who in the last season in which he played for the Lions, at age 30, rushed for 1,491 yards. Neither did Rocky Marciano, who retired with a 49-0 record (and 43 knockouts) at age 32 — at a time when so many of his boxing peers held on as long as they could, often into their 40s. Neither did Isiah Thomas, who was bothered by a painful Achilles tendon injury but still managed to average 6.9 assists per game at age 32.

Bjorn Borg did, sort of, years after walking away from tennis after winning 11 Grand Slams by age 25, but his heart was never in it.

Some do. Often, it isn’t pretty — Magic Johnson’s brief return, Muhammad Ali at the end. Sometimes it’s perfectly glorious: Michael Jordan won half of his six NBA titles after retiring the first time after the 1993 season. Of course, Jordan also returned for a two-season cameo from 2001-03 that was the basketball equivalent of “Godfather 3” — just pretend it never happened.

Maybe this is it for Luck — whom his owner, Jim Irsay, suggested may have left as much as $500 million on the table for his career. Maybe it’s a respite. But even if it was hard to hear the boos, it was easy to understand the underlying reaction. What in the world …

Vac’s Whacks

I spent my vacation in New Hampshire, gluttonously devouring equal parts lobster and “Nights in White Castle,” the latest can’t-put-it-down masterwork from the inimitable Steve Rushin. And if you haven’t yet read “Sting-Ray Afternoons,” make it a two-fer when you order it up.

It’s pretty amazing to think that we in New York will, with any luck at all, be able to see the next 12-15 years of Aaron Judge and Pete Alonso hitting baseballs over the summertime sky. Stereo sluggers, on either end of the Triborough. Yeah. Sign me up for that.

If the NFL had any sense of theater, we would’ve gotten the Bills (4-0 in the preseason!) against the Giants (4-0 in the preseason!) Opening Week rather than making us all wait around an extra week, don’t you think?

Have we really gotten to the point where one bad game in August mathematically eliminated Trevor Lawrence from winning the Heisman? ’Cause he can still play for me.

Whack Back at Vac

Richard Siegelman: The Mets’ modern equivalent of the old Boston Braves’ “Spahn and Sain/And two days of rain” just might be this: “Jake, Jake and Jake (or else hold a wake).”

Vac: Only if you keep noted contact hitter Victor Caratini on the bench.

Kenneth Meltsner: As George Santayana said, “Those who do not learn from the past are doomed to repeat it.” I give you: the coach’s pass interference challenge. Having learned nothing from MLB and a decade of pace-killing NBA replay, this will very likely slow games to a virtual crawl. Typical overreaction to a heinously blown call at worst possible time.

If it’ll make Saints fans stop whining for five minutes, I’ll put up with the hassle.

@NicTatano: Please write on of those “Just Another Guy” columns about Marcus Stroman.

@MikeVacc: Some things are beyond even my considerable powers.

Steve Giegerich: Cricket players. The Players Weekend uniforms made the baseball players look like cricket players! Bill Veeck is laughing at us and waving his wooden leg at this nonsense.

Vac: Are we sure that the man who gave the world 3-foot, 7-inch Eddie Gaedel wouldn’t be first in line to endorse those Spy Versus Spy outfits?