The Domaine de Praden stadium, which had just been refurbished, was taken over by travellers on Sunday afternoon.
They forced the lock to the stadium open, and plugged themselves into the electricity and water. The two guards on duty were reportedly helpless.
Local Mayor, William Portal, said: “In 25 years of working at the town hall, I have never seen anything like this.
“We have always been able to negotiate [with the travelling community] an appropriate area for them to set up camp, we just ask that their children are sent to school and they use the rubbish containers provided.
“So we never imagined anything like this could ever happen.”
Damage to the grass and sprinkler system, as well as other repairs, is expected to cost up to €50,000.
Local footballers have also been put out by the invasion – training was supposed to start again on Monday, and matched on August 19.