LAS VEGAS — Shawn Porter’s final moments in the ring showed why he had to walk away.

Following his second knockdown in the 10th round of Saturday’s WBO welterweight championship fight against Terence Crawford, Porter scowled and repeatedly smacked the canvas with his gloves as referee Celestino Ruiz issued an 8-count.

With his father and trainer, Kenny, seconds away from stopping the fight, Shawn wasn’t hurt as much as he was angry. Even on his knees, under duress as a result of being caught by one of the world’s best boxers, the competitive fire burned even as he knew it was going to be extinguished.

The former welterweight champion announced his retirement during the postfight news conference, a development that he said was predetermined no matter the outcome. But it was perhaps reinforced by the loss.

Porter had too much pride, too much ambition to be relegated to a tier below the best. And that willingness to pursue greatness, in an era when that is noticeably absent, will be a lasting part of his legacy.

“After you’ve fought everybody at the top, what more do you do?” Porter said. “I’m not going to be a gatekeeper. You would look at the four losses and assume, ‘Well, he could be a gatekeeper now.’ It’s not the life that I want to live.”

Porter (31-4-1, 17 KOs) retires as a two-time welterweight champion who faced the best competition of his era. That includes Crawford (38-0, 29 KOs), who picked up the biggest win of his title run in the 147-pound division.

As Porter elaborated on his decision to retire, it became apparent the decision was not impulsive but meticulously mapped out. The 34-year-old revealed he initially wanted to step away from the sport following his split-decision loss to Errol Spence Jr. in 2019. Porter said that was plan dating all the way back to 2017.

But something felt amiss.

“After we fought, I felt like there was something else,” Porter said. “And something else was Terence Crawford.”

Porter proved to be the toughest test for Crawford as a welterweight. Porter’s trademark pressure and unwillingness to be baited into opportunities for heavy counter shots helped him win rounds early in the fight. In fact, Crawford led by just one point heading into the 10th round.

But after a knockdown off a quick hook, then another in the middle of the round — that one off a punishing overhand right — Kenny Porter had seen enough. The Porter father-son combination were well aware of Crawford’s reputation as one of boxing’s nastiest fighters and a clinical finisher. There was no reason, in Kenny’s eyes, to let it reach that point.

Kenny had no idea Shawn was going to retire, no matter what happened at the Michelob Ultra Arena at Mandalay Bay. Shawn and Kenny never had that conversation.

But perhaps paternal instincts kicked in as Kenny ascended the stairs, stepped onto the canvas and asked for the fight to be over. The trainer and father was thinking about being able to drive over to his son’s house, visit and play with his grandchildren.

“In the biggest part of this picture, when this thing is over with, I’m still his father, he’s still my son,” Kenny Porter said. “And we get to do that part. That’s a long life of that.”

Even though thoughts of retirement percolated in Shawn’s head for years, it didn’t become clear until a recent interaction with retired champion Andre Ward.

During their work as analysts for the Tyson Fury-Deontay Wilder trilogy fight in October, a fan came up to Ward and asked him about the hypothetical matchup against Canelo Alvarez, ESPN’s No. 1 pound-for-pound fighter.

The fan told Ward he still had one more fight left in him. According to Porter, Ward’s response was simple.

“He said, ‘Why can’t I just have one more left in me?'” Porter said. “And the guy was confused. Meanwhile, I’m like, he set it off right there. Why do I have to continue? Why can’t I just have one more in me and save it?”

Porter never wanted to be someone who fought into his 40s. He even pondered hanging up the gloves around the age of 30.

But he kept going, pushing himself and testing his skills against the best in the world. Even if he had won, he decided that he had had enough. His health is still intact and he is at the beginning of a promising TV career.

Porter extracted everything he possibly could out of his career, giving fans entertaining and memorable fights along the way. And even as he announced his departure, that was at the forefront of his mind, a reminder of the legacy he leaves.

Said Porter: “I hope that you guys got everything that you expected to get from this fight.”