Kyrgios wore a red cap to Wimbledon. Here’s why that’s controversial.

Throughout Sunday’s three-hour Wimbledon final, Nick Kyrgios was on his best behavior — at least when it came to the tennis tournament’s notoriously strict dress code. Then it came time to accept his trophy.

For that occasion, which took place minutes after the Australian lost in four sets to defending champion Novak Djokovic, Kyrgios swapped out his white cap for a bright red Nike Jordan cap, a move that flouted nearly a century and a half of tournament tradition calling for players to wear white clothing on court.

The Duchess of Cambridge, who handed Kyrgios his runner-up trophy, did not noticeably react to Kyrgios’s faux pas. 

Other observers, however, were astonished — especially because Kyrgios had gotten flak after donning the red cap earlier in the tournament.

One journalist called the move Kyrgios’s “final act of defiance.” Others pointed out that Kyrgios might get fined. As of early Monday, a Wimbledon spokeswoman was unable to confirm whether Kyrgios had been penalized.

The rule that players wear white on the tennis court dates to the tournament’s beginning, in 1877. At that time, it was generally believed that sweating was improper and that white clothing would either curb a player’s perspiration or hide it, Time reported.

 Yet as times have changed, the dress code at Wimbledon has not eased up. In fact, it has become stricter, with tournament officials even checking the color of players’ underwear during matches.

Now, the rule is that players must wear “suitable tennis attire that is almost entirely white … from the point at which the player enters the court surround.

Acceptable clothing “does not include off white or cream,” and colored trim around the neckline or sleeves “must be no wider than one centimetre.” There are other highly specific guidelines, although some players this year were allowed to wear colors supporting Ukraine.

Far from its sweat-phobic origins, Wimbledon has more recently embraced the all-white rule as a “great leveler” and a way for “letting the tennis and the players stand out,” rather than their clothing.

But even the game’s finest champions have challenged the rule. Roger Federer, an eight-time Wimbledon winner, said in 2014 that a dramatic tightening of the dress code that year was “too strict,” the New York Times reported. A year earlier, Federer was forced to change his shoes after he wore a pair with orange soles during his first-round match, according to the Associated Press.