Thieves left golfers bunkered when they went on a rampage at Leyland Golf Club.
The crooks stole 15 flags from greens across the 18-hole course.
Colin Burgess, a professional at the club, said: “The flags are about eight foot tall so it wouldn’t have been an easy job.
“It’s not something one person could have done. You would have to cover quite a few hundred yards to take them all.”
Mr Burgess said there have been similar incidents in the past at the course, on Wigan Road, but never on this scale.
The latest incident happened between 9pm on July 15 and 5.30am the following morning. The thieves did not take the three flags closest to the club house.
Mr Burgess said: “The odd one can go missing at night but you normally find them dumped nearby.
“None of these have turned up. It’s like a playground on here at times. The flags are not cheap either, they cost about £20 each.
“They are not just a wooden cane with a flag on top, they are made out of fibreglass. The ground keeper turned up on Saturday morning to find the flags missing.
“It was annoying because it meant they had to go back in and get new flags, and then put them on the course.”
A spokesman for Lancashire Police said they were investigating the theft and had spoken to staff at the golf club about crime prevention.
He added: “Officers visited the scene and staff have reported problems in the past with youths on the footpaths surrounding the course. Police searched the immediate area but didn’t find anything.”
The flags are described as a fibreglass pole with yellow and red flags on the end, with Leyland Golf Club written on the side.
The police spokesman said: “This may have been done for a joke and they may have later been dumped.”
Call police on 0845 1253545.