Regardless of when you are reading this, odds are you know a football fan who believes Jim Brown is the greatest player in history. From 1957 through 1965, there was no better ball-carrier than the Cleveland Browns icon who made the Pro Bowl in all nine of his seasons. Brown led the league in rushing on eight occasions, he finished atop the rushing touchdowns category five times and he won MVP honors in 1957, 1958 and 1965. In 1964, Brown helped Cleveland win the NFL championship, something the Browns failed to accomplish from 1965 through (at least) the end of the 2018 campaign. 

Brown rushed for over 1,500 yards and 17 touchdowns in 1965, and he was at the peak of his career when he retired in July 1966. He had already entered the world of acting while still a player and was on the set of The Dirty Dozen when he announced the end of his career. Per Dawg Pound Daily, Brown’s filming schedule led to him missing training camp, which irritated team owner Art Modell. It’s possible, perhaps likely, Brown would’ve played at least one more year had Modell not threatened to fine his star player for missing meaningless practices.

As explained by the International Tennis Hall of Fame, Bjorn Borg made history when he became the youngest male to win the French Open title in 1974. When he lifted that tournament’s trophy a sixth time in 1981, he had won his 11th major championship, a record for the Open Era at the time. Borg’s rivalry with John McEnroe, spotlighted in the film Borg vs. McEnroe, remains one of the sport’s greatest on-the-court feuds, as they faced off 14 times from 1978 through 1981. According to Ubitennis, both men won seven of those matches. 

At the age of 26, the cool and often quiet Borg stunningly announced his retirement in 1983. McEnroe tried to convince his rival to reconsider, and Borg eventually attempted a comeback in the early 1990s, during which he failed to cover himself in glory. By ’81, however, the all-time tennis great with a rock star look and his own groupies who attended tournaments was burned out to the point that he admittedly didn’t care all that much about losing, even to McEnroe. The only significant accomplishment missing on his resume at the end of his career was a US Open championship (he only played in an Australian Open once, which he did at the age of 17). 

Wide receiver Calvin Johnson played for some dreadful Detroit Lions teams during his nine-season career. The 2008 Lions went 0-16, and the franchise made the playoffs a total of three times from 2007 through 2015. Johnson wasn’t to blame for his team’s failures, though, as the six-time Pro Bowl wideout led the NFL in receiving touchdowns in 2008 (12), finished the 2012 campaign as the league’s leader in catches and set a record that year by tallying 1,964 receiving yards. In 2015, Megatron caught 88 passes for over 1,200 receiving yards, and he found the end zone nine times. 

The following March, Johnson retired at the age of 30, relatively young for a healthy wide receiver with his physical attributes. “My biggest regret is that I wasn’t able to help give our fans a championship,” Johnson admitted via an official team statement, per the Detroit Free Press. As explained by ESPN, only Torry Holt and Jerry Rice accumulated more receiving yards over nine seasons than Johnson, and Johnson retired with more receiving yards and receiving scores than any other NFL player who never won a single playoff contest. 

Chris Borland’s ceiling touched the stars after the 2014 season. The linebacker selected by the San Francisco 49ers in the third round of the NFL Draft appeared in 14 games, made eight starts and became a cornerstone for his team’s defense. The NFL named Borland Defensive Player of the Month for November after he won Rookie of the Week twice that month. 

An ankle injury prematurely ended his debut campaign before Christmas Day, but there was no indication that setback would affect him ahead of San Francisco’s subsequent training camp. The Pro Football Writers Association named Borland to its All-Rookie Team following the season. 

In March 2015, a fully-fit Borland retired from the NFL before his 25th birthday. Per NFL.com, Borland explained on ESPN’s Outside the Lines that he believed he’d suffered three concussions during his life, and that worries about the effects of head trauma resulted in his decision to permanently end his career. He turned to a life of social activism, and, as detailed by NPR, he called upon the Catholic Church to champion additional gun control laws in the United States in the summer of 2019. 

Any conversation about the greatest heavyweight boxers in history had better include Rocky Marciano, or it’s for naught. From 1947 through September 1955, “The Brockton Blockbuster” won all 49 of his professional bouts, and 43 of those victories came via knockout. In September 1952, Marciano won the world heavyweight championship after he dropped then-champion Jersey Joe Walcott in the 13th round of a match Walcott was winning on the scorecards. Marciano held the heavyweight crown past his 32nd birthday and his win over Archie Moore in September 1955. 

With a potential rematch versus Moore looming, Marciano retired an unbeaten champion in April 1956. Per ESPN, the original “Rock” (apologies to Dwayne Johnson) remains the only undefeated heavyweight champion to exit the sport with an unblemished record. According to The Independent, Marciano rejected numerous offers to return to the ring, minus a “heavily choreographed” closed-door session with Muhammad Ali in 1969. That same year, Marciano was killed in a plane crash just one day before celebrating his 46th birthday. According to Boxing Monthly, human error and avoidable mistakes resulted in Marciano’s untimely death.

Decades before Michael Phelps established himself as the most decorated Olympic swimmer in history, Mark Spitz became a household name for his performances at the 1972 Summer Games. After he earned a pair of team golds in 1968, Spitz won a record seven gold medals (Phelps topped that mark by winning eight golds in 2008) in Munich — four individual and three team — and the brash and outspoken American known for sporting his trademark mustache retired soon after those Olympics at the age of 22 to cash-in on his fame through endorsement deals and other business opportunities. 

“I retired because I didn’t have a future in swimming because we couldn’t make money,” Spitz admitted during an interview in 2011. “The rules were different back then than they are today.” As noted by ESPN, Spitz was accused of “blatant commercialism” by the Soviets after he waved his shoes toward the crowd while on the medal stand at the ’72 Games. Nobody imagined at the time millionaire NBA players would be allowed to feature in an Olympic basketball tournament decades later. 

According to the International Swimming Hall of Fame, Spitz held 33 official and recognized world records upon his retirement. ESPN ultimately named him 33rd on their list of the 50 greatest North American athletes of the century.