As Andrew Luck, dressed in street clothes, walked off the field at Lucas Oil Stadium presumably for the last time — as news of his impending retirement had already leaked — some disgruntled Indianapolis Colts fans let their star quarterback, renowned for his toughness through a myriad of injuries, know what they thought of the decision.

That’s how much of a shocker this was. The news had spread quickly, and disbelief reverberated throughout the country as Luck, once considered to be the next big thing in the NFL, one deemed promising enough to boot Peyton Manning out of the franchise he led to a Super Bowl title, was suddenly done.

Sure, he has dealt with his share of injuries over the past few years, including injuries to his ribs, abdomen, kidney, throwing shoulder and head (concussion). And yes, his current status was up in the air due to a mysterious calf/ankle issue. But this was a quarterback who, just last season, led the Colts to a 10-6 regular-season record and a playoff win. In today’s pass-centric era of football — in which you can barely touch the quarterback — it seemed like he had plenty more left in his tank.

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Yet, he didn’t, as Luck decided he’d rather forfeit the $21.1 million salary he was set to earn in 2019 than slog through the mental grind of getting ready to play football again, a fact that apparently tweaked some fans enough to boo.

“It hurt — I’ll be honest, it hurt,” Luck said referring to the reaction.

Those fans were booing because they knew that a Pro Bowl quarterback’s sudden decision to retire two weeks before the regular season would leave a team in the lurch. And to be sure, the Colts may still be hard-pressed to reach their ceiling in 2019, a season in which they need to reach the AFC title game to build on last season’s accomplishments.

But the NFL is the ultimate next man up league, and there are some reasons to believe Indianapolis will still be in solid hands this season, since this doomsday scenario is one of the reasons quarterback Jacoby Brissett — who started 15 games for Indianapolis in 2017 but was relegated to the bench due to Luck’s return from a shoulder injury in 2018 — remains a Colt.

Colts turn to Jacoby Brissett, a former Tom Brady understudy

After all, given Luck’s injury history, general manager Chris Ballard knew he couldn’t afford to give away Brissett this offseason, even with the 26-year-old entering a contract season and set to be a free agent next March.

“A year ago we got some calls, this year we got some calls — nothing that was tangible enough for me to say [yes],” Ballard told Yahoo Sports during a training camp visit earlier this month. “Not only is he a good player, but Jacoby adds value just with his presence. And I don’t ever undervalue that.”

And while the rest of the country was caught off guard by Luck’s decision, chances are good that Brissett — who was held out of the Colts’ third preseason game on Thursday night as an injury precaution — will be ready for the opportunity, thanks to a lesson he learned as Tom Brady’s understudy in 2016.

“I learned preparation — the way he prepares and approaches the game — to always be ready for those unknown moments,” Brissett told Yahoo Sports during a recent phone interview. “I think he’s probably excelled at that, probably, more than anybody that’s ever played this game … it’s always having a plan, and knowing his plan inside and out so that he can be ready for when those unknown moments come.”

So to get ready for this season, Brissett — who has taken practically all of the first-team snaps in organized team activities and training camp as Luck battled his ailments — attacked it with a simple approach.

“Just do as I’ve always done — prepared as if I’m the starter, no matter what,” Brissett said. “And that won’t change, no matter what year I am, or whether it’s a contract year or not. So I just want to keep that approach.”

Brady, of course, is accustomed to hard coaching under Bill Belichick, which Brissett — a third-round pick of the Patriots in 2016 — got to witness for a full year before his trade to Indianapolis.

“It’s just really being vulnerable in those meetings and in practice and being able to take coaching, take criticism and be able to take it from the classroom to the field,” Brissett told Yahoo Sports.

The Colts have been happy with Brissett’s overall progress and his ability to rally his teammates around him, even before they knew he’d have to be the full-time guy.

“He’s got a calmness about him a lot of guys don’t have,” Ballard said.

Ballard noted that Brissett has a knack for connecting with people — “he has high emotional intelligence,” he added — and the Colts were also happy with the work he has done on his mechanics to improve his accuracy.

With Luck suddenly out of the picture, Indianapolis will surely need Brissett to be better than he was in 2017, when he completed nearly 59 percent of his passes for 3,098 yards, tallied 17 total touchdowns, and tossed seven interceptions while taking a league-high 52 sacks. The Colts better hope he is, because charting a path forward would sure be easier that way.

In a perfect world, Brissett will play well this season and the Colts — an ascending team with one of the league’s best young offensive lines, best offensive head coaches (Frank Reich) and best young defensive coordinators (Matt Eberflus) — will pay him and keep moving forward.

The alternative to that is much less palatable, as it would surely include more boos — and more losses — during a trip to the NFL quarterback wilderness, a place that can take years to get out from under (just ask the Miami Dolphins or Cleveland Browns). It’s clear Ballard, who is widely respected for his football acumen, would like to avoid the latter scenario.

Perhaps in retrospect, Ballard’s answer — when asked if he has resigned himself to losing Brissett in free agency next March — is not only instructive about how the Colts feel about Brissett, but also how they knew there may come a day they’d end up relying on him.

“Let’s let things play out — the one thing I don’t ever want to do is work in hypotheticals to where we’re writing the end of the story before the story has even started,” Ballard said. “I do think a lot of Jacoby Brissett and what he means for us.”

And now, we’ll get a chance to see why.

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