NEW YORK (AP) — The U.S. Open added more members of the police, including undercover officers, on Friday, a day after four environmental activists in the Arthur Ashe Stadium stands caused a 50-minute delay during Coco Gauff’s women’s semifinal victory.

One protester glued his bare feet to the concrete floor of an upper level during Coco Gauff's women's semifinal victory.

U.S. Tennis Association spokesman Chris Widmaier said there are more uniformed and undercover police officers around the entrance gates and at the courts. The tournament also was going to increase the frequency of messages on arena videoboards telling spectators how to contact U.S. Open security if they see anything unusual.

NYPD and medical personnel removed the man whose feet were stuck to the ground in the Ashe stands. All four activists were taken into police custody.

A group called Extinction Rebellion said it was responsible for the protest.

According to Widmaier, the four protesters were told they are not allowed to return to the U.S. Open during the rest of the tournament. He said they could face fines or criminal charges if they are found on the tournament grounds.

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