Environmental activists briefly interrupted play at the British Open on Friday by throwing an orange substance to the side of the 17th green at Royal Liverpool, prompting American player Billy Horschel to intervene.
Police and security guards quickly took action to keep the Just Stop Oil protesters from causing a bigger disruption during the second round. Play resumed not long after the protesters were removed.
Horschel was playing the hole at the time and helped a greenside marshal lead one of the protesters away. The other players at the 17th were Corey Conners and Alex Noren. They were marking their balls and getting ready to hit their second shots when the disruption started. All three players made par on the hole.
Organizers cleaned the affected area before the next group hit their tee shots.
The protesters, wearing white shirts with the words "Just Stop Oil," had entered from each side of the elevated green that sits with the Irish Sea in the background. One of them had a flare, police said.
Two protesters were immediately taken away from the green, while two others were later escorted away separately.
Local police said in a statement that two men and two women were detained "on suspicion of conspiracy to commit criminal damage and public nuisance."
Just Stop Oil is an organization that wants the British government to stop new oil, gas and coal projects. It has interrupted a slew of major sporting events in Britain in recent months, including Wimbledon, an Ashes cricket test and the world snooker championship.
British Open organizers said ahead of the tournament they were aware of the possibility of the protesters trying to disrupt the Open but had "significant security procedures in place." It had advised players not to get involved.
The 17th hole attracted most of the attention ahead of the Open after being redesigned to add drama to the tournament. It is listed at only 136 yards but its elevated green challenges players with steep slopes and deep bunkers.
The British Open started Thursday and is scheduled to finish on Sunday.