In 1979, Lyle Alzado boxed against Muhammad Ali. Seriously

This offseason, Shutdown Corner will travel down memory lane with a series of stories presenting some interesting and sometimes forgotten stories from the NFL's past. Join us as we relive some of the greatest and craziest moments in the sport's history.

These days, when an All-Pro NFL defensive player has a contract dispute, he goes on "Dancing With The Stars."

Lyle Alzado handled his by boxing against Muhammad Ali.

There are so many strange tales in NFL history that it's impossible to single one out as the strangest, but Alzado fighting Ali at Mile High Stadium on July 14, 1979 is hard to beat.

Alzado was a 30-year-old star defensive end for the Denver Broncos, coming off an All-Pro season in 1977 and Pro Bowls in 1977 and 1978. He also had fully earned his reputation as a wild man and was having a contract dispute with the Broncos.

Ali was 37, less than a year removed from winning back the heavyweight title from Leon Spinks. Ali was retired, though he'd come back to regrettably fight Larry Holmes in 1980. After a planned exhibition for Ali against boxer Jimmy Ellis fell through, Alzado got a call from Denver boxing promoter Lyle Pedersen.

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"Lyle Pedersen called me and said, ‘Would you like to fight Muhammad Ali?’" Alzado said, according to a UPI report before the fight. "I thought it was a joke. But it wasn’t. We’re going to fight."

It's inconceivable this actually happened. The most famous boxer ever fought a star NFL player, days before Alzado was to report to training camp, in an eight-round exhibition match. Even for Alzado, whose personality was as outlandish as any man who has ever played in the NFL, this was nuts.

“I don’t want to go in there and get my head knocked off,” Alzado told UPI. "But to be very honest with you, without meaning to sound cocky, I’ve never been afraid of any man in my life.”

What makes it even crazier is that Alzado put up his house as collateral, to cover the promotional costs.

"When Denver writers belittled the exhibition and ripped him for saying he could lose his house – which he had put up for collateral for the promotional costs – if Denver fans didn’t step up and buy tickets, that was unfair. It was true," Terry Frei wrote in his book, "77: Denver, The Broncos, and a Coming of Age." "His restaurant was in huge trouble, and he was on the way to financial oblivion." It wasn't like players in the late 1970s made the crazy salaries of players today; Alzado was said to have been making $90,000 annually from the Broncos, and wanted $200,000 a year. He was supposed to make $100,000 for the Ali fight.

Alzado had some boxing chops. He was reportedly a Golden Gloves champ with a 44-1 amateur record. And while Frei wrote that Alzado admitted later the fight was for "an economic venture and getting contract leverage," before the fight Alzado played up the possibility of quitting football and becoming a professional boxer. The fight was on Saturday. The Broncos' veterans were set to report to training camp late the following week. Alzado said right after the fight that he'd let the Broncos know in a few days if he was going to retire from football to be a boxer.

“I’ve always dreamed of being heavyweight champion of the world,” Alzado told the AP after the fight. “I don’t want to go into the ring publicized as ‘the great white hope.’ It sounds corny, but I just want to bring the heavyweight title to Colorado.”

Yes, this all actually happened. Someone figured it would be a good idea to have the fight outdoors in the middle of July, so Ali and Alzado fought in blistering heat under the midday sun at Mile High Stadium. The fight itself wasn't pretty, though Alzado looked a lot better than you'd expect from a defensive end boxing the great Ali. Ali clearly wasn't in great shape — he said he didn't train for the fight — and spent a lot of the bout playing to the crowd and making sure Alzado didn't somehow make him look bad. Alzado tried hard in the unscored exhibition and got some nice compliments from "The Greatest."

“For a non-fighter he’s great,” Ali said, according to the AP. “He’s got the potential to be a world champion in the next two years if he continues to improve. For a man to come into my league and almost master me was a surprise.”

Financially, the bout was a nightmare. The broadcasters said Alzado hoped to get 50,000 or even 60,000 people to watch the fight. Reporters there estimated the crowd at 20,000, but only 11,128 paying fans were in attendance (I get it was a farce, but there weren't more people in Denver who wanted to see Ali in person?) according to UPI. The fight made about $209,000 and Ali was guaranteed $250,000. Alzado was supposed to make $100,000, but ended up with nothing. Nine years later the promoters and Alzado were still fighting a legal battle all the way to the Colorado Supreme Court, over money owed. A jury awarded Alzado $92,500 but an appeals court reversed the decision and the Colorado Supreme Court affirmed that reversal. To make this strange story even stranger, that case is now studied in business law textbooks. There is no definitive word on if Alzado lost his house over the fight.

The fight was also the last time Alzado appeared at Mile High Stadium as a hometown hero. He reported to Broncos camp right after the fight, but then walked out claiming again he was considering a boxing career. The Broncos traded him to the Cleveland Browns in mid-August. He immediately signed a five-year deal with the Browns. After three Browns seasons, Alzado moved on to the Oakland/Los Angeles Raiders and was part of a Super Bowl championship team. He died in 1992, at age 43, after admitting to steroid abuse during his career.

Alzado is one of the wildest characters in NFL history. The Alzado episode of NFL Network's "A Football Life" might be the best of that entire fantastic series. It's impossible to picture an NFL star in today's world challenging a great fighter to a bout. Can you imagine if Von Miller agreed to an exhibition fight against Conor McGregor this offseason?

Really, no other player back in the 1970s was crazy enough to fight Ali either. Just Alzado.

Previous Shutdown Corner NFL throwback stories: Joe Montana's underrated toughness | Barry Sanders' long-forgotten final game | Jake Delhomme's playoff nightmare | Barry Switzer, outspoken as ever | Was Sebastian Janikowski worth a first-round pick? | How Jim Harbaugh punching Jim Kelly helped Colts land Peyton Manning | Jay Cutler makes the greatest throw ever | "Has anyone ever kissed your Super Bowl rings?" | How the Patriots once faced a fourth-and-63 | The Packers survived a miserable two-decade run | "NFL PrimeTime" changed how we watch football | One of pro football's greatest games happened in the crazy USFL | The time Warren Moon should have had 650 yards in an NFL game

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Frank Schwab is the editor of Shutdown Corner on Yahoo Sports. Have a tip? Email him at shutdown.corner@yahoo.com or follow him on Twitter! Follow @YahooSchwab