Less than two months after earning rights to share the new Martha's Vineyard Skatepark, bikers are once again being told to keep out.

The reversal came Monday night during an emotional parks department meeting moments after commissioners heard pleas from teenage bikers anxious to stay in the park. In the end, commissioners bowed to the advice of Oak Bluffs' insurance agent and town counsel to ban bikers.

"It's been a difficult and controversial issue for us all," said Richard Combra Jr., chairman of the park commission. "I've been on this board for 13 years, and nothing has been this hard."

Allowing bikers to practice tricks in the same half-acre concrete park skateboarders dominate puts the town's insurance coverage at risk, said Don Lambert of Lambert Insurance Agency.

"It is the insurance carrier's position that they will either cancel the town's liability policy or exclude coverage for the park entirely if bikes are allowed into the park," said Mr. Lambert in a letter to town counsel.

"It is my opinion that it would be impossible to replace [skatepark coverage] and may well jeopardize the town's entire liability coverage," he continued.

Biker use at the park has been an issue since it opened last fall. After being kicked out of the park repeatedly, a number of bikers and their parents pushed the Oak Bluffs park commissioners to change the policy. In February, despite resistance from some skateboarders and the volunteers who raised funds to build the park, the commissioners opened the door to bikers.

Tuesday afternoon, a freshly painted "No Biking" notice already appeared under the skatepark's rules. By the time school got out Tuesday and more than 20 skateboarders had flocked to the park, word of the new biker ban had already reached all corners. Skateboarders expressed mixed emotions. Some, like Ricky Corwin, cheered, saying that the bikers got in the way, especially the youngest among them.

"You don't want to say anything because they are your friends," said Mr. Corwin, who hung back against the chain-link fence watching other skaters flip their boards.

Others skateboarders felt sorry for the bikers - remembering what it felt like to not have a place to practice tricks.

"Experienced bikers deserve to be here. In the summer, though, my opinion might be different," said Elliott Vecchia, who said he was friends with the handful of bikers who had been hanging out there over the last month.

Adam Downing, one of the half-dozen regular bikers, left his BMX at home Tuesday and tried his luck on a skateboard. Adam, who said he'd rather be biking, admitted he would find his way back to Edgartown parking lots and ride until the police chased him away.

Other bikers like Ben Jones, one of the high schoolers who attended the park commission meeting the previous night, just went home after school on Tuesday, though the brisk spring weather made him wish he were riding at the skatepark.

"This is the worst thing ever. I felt pretty confident that we wouldn't be kicked out. I started to feel like everyone was on our side," Mr. Jones said.

Candace Nichols, an attorney who got involved with the biker cause because of her sons' friends, said that adults, not kids, staged the turf battles.

"I think there are a lot of public desires and prejudices that are being confused with public policy. Kids aren't having any problems, so adults shouldn't be chasing them away," she told park commissioners Monday night.

Later this week, Ms. Nichols said her group would explore the insurance issue further - checking in with the six other skateparks in Massachusetts that accept bikers. But to build an entirely separate park for bikers would be wasteful, she said.

"Why spend double to amount of money, double the insurance, double the time when the kids are getting along. Just because a small group of people doesn't want it is not reason to build a second park," Ms. Nichols said.

The biker invasion has been a tough issue for MV Skatepark Association officials, the volunteer group spearheading the skatepark initiative. The board of directors, president Elaine Barse said, is divided over whether bikers should use a park they worked for eight years to fund and build.

"I understand [the bikers] are having fun at this park, but it wasn't designed for bikes. Is it appropriate for a kid with training wheels to be in that space? It opened up a can of worms, and the answers aren't there yet," said Ms. Barse.

Monday night, unaware the commissioners were about to reinstate a ban on bikes, Ms. Barse requested that the park commissioners prohibit bikes for a year in order for the association to study wear and tear on the equipment.

"We really need to see how this will work with summer coming up and how much use it's going to get," said Ms. Barse in a conversation Tuesday. "We only had two and a half months before the bikers came. We didn't feel it was an accurate representation of what would actually happen to the park over time."

Over the last month, a piece of granite copping broke off the far corner of the raised rim. Most are pointing fingers at the bikers, but no one has stepped forward to take the blame.

The park commissioners fielded a number of complaints from community members concerned about the safety of mixing bikers with skateboarders, Mr. Combra said.

Final policy decisions for the park rest on the shoulders of Oak Bluffs park commissioners, who offered to manage and supervise the skatepark along with the town's other recreational parks. The land is being leased from the Martha's Vineyard Regional High School, and skatepark association volunteers secured more than $40,000 needed to construct the park.

"We're trying to do a positive thing here. Anybody that ever held a bake sale or threw money in a kitty jar wanted to do something good. Sometimes we lose sight of that. We're feeling like bad guys," said Ms. Barse.