With surveillance cameras rolling and officers in hiding, police cracked down Sunday on 21 dirt bike and ATV fanatics they claim have been tearing up an industrial park in Walpole while boozing and smoking pot — outings that Boston Bike Life counters are simply old-fashioned family fun.

“These vehicles were observed doing wheelies, burnouts, operating at a high rate of speed, driving on and off the road, even crashing in the middle of the road. Many of the operators were not wearing helmets and none of the off-road vehicles were registered or insured,” Walpole police officer Matthew A. Crown stated in his report.

Fourteen of the group’s alleged affiliates, aged 18 to 41, pleaded not guilty yesterday in Wrentham District Court to charges including trespassing, disorderly conduct and negligent operation. Judge Stephen S. Ostrach repeatedly threatened to throw them out of his courtroom for talking, applauding and clowning around. He released most on personal recognizance, but also set bail as high as $2,500 for those with open court cases and in violation of their probations. All were ordered to stay away from the Renmar Avenue playground and to return before him July 20 for a pre-trial hearing.

“These are not insignificant matters like, say, an overdue library book,” Ostrach sternly warned the defendants.

Four women and three juveniles also rounded up in the stunt-ride sting by Walpole, Boston and state Environmental Police, and the National Insurance Crime Bureau and the Metropolitan Law Enforcement Council will be summonsed to court at a later date. The club’s caravan — five personal vehicles, 11 off-road vehicles and the rented box truck used to transport dirt bikes and ATVs to the site — were impounded, Boston police said.

Assistant Norfolk District Attorney Rachel Audley said police have fielded “many calls from concerned residents” about the off-road antics, which she said have taken place in the past year on private property in Walpole marked as no trespassing.

Officer Crown said in his report, “Along with the dangerous driving, many parties had been observed drinking alcohol from open containers in public, smoking marijuana and trespassing on private property.”

But attorney Edward Sweeney, representing one of the defendants, argued, “It’s off-road biking. No one ever told them to not show up. After a while, they just thought it was acceptable. It was a Sunday afternoon. There were children present. It was almost as if it were a family outing.”