A protester lit the court and his arm on fire during a match at the Laver Cup tennis event Friday, briefly delaying the start of the second set between Stefanos Tsitsipas and Diego Schwartzman at the O2 Arena.
The activist, carrying a lighter and wearing a white T-shirt with a message about private jets, made his way onto the black court and sat down near the net. The person eventually was carried away by security guards.
"It came out of nowhere. ... I never had an incident like this happen on court," Tsitsipas, the runner-up at the 2021 French Open, said afterward. "I hope he's all right."
Tsitsipas spoke to the chair umpire to make sure it would be safe to continue play and asked that a mark left on the court be cleaned up.
"A man accessed the court this afternoon and was promptly removed by security," the Laver Cup said in a statement. "Play was stopped briefly, he has been arrested and the situation is being handled by the police."
Tsitsipas recorded a 6-2, 6-1 victory for Team Europe over Team World's Schwartzman to give his team a 2-0 lead in the competition.
Federer, 41, hasn't played an official match since Wimbledon in July 2021 and is ending his playing career after a series of operations on his right knee.
There have been other instances of high-profile tennis matches being interrupted in recent years, including during the 2009 final at Roland Garros, when a man went up to Federer and tried to put a hat on his head.
At this year's French Open, in June, a protester wearing a T-shirt with the message, "We have 1028 days left," interrupted the men's semifinal between Casper Ruud and 2014 US Open champion Marin Cilic by attaching herself to the net with metal wires and glue and kneeling on the court.
The Associated Press contributed to this report.