"We've got 220 people playing football every Thursday afternoon ... It only takes one person to be injured and it's all over," he said.
Fortunately, however, Northland CCTV was a major sponsor of the club and had installed state-of-the-art security cameras.
Within an hour of downloading the footage on Monday, which showed the perpetrator had also tried to force his way into the clubrooms, a repentant 12-year-old boy was at the Kerikeri police station with his mother.
Other incidents in recent months included a group of girls smashing bottles on the concrete outside the clubrooms. They had also been identified thanks to CCTV.
Mr Roberts, a constable with Kerikeri police, said the groundsman gave the pitch a tight cut before the weekend to hopefully get the last of the glass out.
"We just ask people to respect the building and the field. And if they do vandalise it, they will get caught. The CCTV is really, really good."