Security was forced to rush onto the tennis court Friday at the O2 Arena in London after a man set his arm on fire.
The arena is hosting the Laver Cup, which will be Roger Federer's final professional competition.
The apparent climate change activist ran onto the court wearing a shirt that said, "END UK PRIVATE JETS."
Security quickly intervened and the man was arrested, according to the BBC.
"It came out of nowhere," said Stephanos Tsitsipas, who was playing Diego Schwartzman when the match was interrupted. "I never had an incident like this happen on court. I hope he is all right."
Play eventually continued, and Tsitsipas went on to win the match.
The biggest stars in tennis, including Rafael Nadal and Novak Djokovic, are participating in the Laver Cup as Federer prepares to retire.
Federer is teaming up with Nadal on Friday for his final professional match. The two are taking on the American team of Jack Sock and Frances Tiafoe.