Members of a sports club had to clear the pitches of empty liquor containers and other trash when they arrived for morning practice.
Rubbish on the grounds of Thomas Hardye School in Dorchester was reportedly left by young people who had gathered there on Friday evening.
The police had to go to the scene a few times during the evening.
The incident prompted a police warning to parents.
A Dorchester Police spokesman said on Saturday: “Last night groups of young people gathered at the grounds of Thomas Hardye.
“The police came and the majority fled, but a few stayed and spoke to an officer. They picked up the rubbish there and left the area as instructed.
“The area was later patrolled by other neighborhood officers and again the youths moved away from the area.
“This morning (Saturday) a sports club was present and had to clear the locations of empty bottles, cans, bottle caps and other general rubbish before they could safely start the sports session.
“The photos (were taken) after most of the trash had been picked up.”
The spokesperson added: “Do you know where your children are? Could your child have been involved in this antisocial behavior?
“Dorchester Neighborhood Officers will continue to patrol and move people who drink alcohol off school property.”