The group moved to the other side of the plaza, directly across from the 23rd Police Precinct. Facing a row of mini-cruisers, Ari, who was in sixth grade and lives in Brooklyn, stood at the end of one long block of marble. In front of him was another block; between the two, a gap.

Ari wore look of stern focus and clothes flowed from Volcom and Adidas.

His dad hung back with Mr. Rodriguez. They talked about street skating and the hazards of being kicked out of public spaces. “I grew up dealing with cops almost every day,” Mr. Misurelli said, adding that he raised his son to be respectful and to avoid confrontation.

“They’re not legally allowed to touch us,” Ari said.

“Kids nowadays know that,” said his dad. “Back then, they could touch you.”

Standing atop the long marble block, Ari jolted into motion, rolling to the end and popping a kick-flip over the gap. He landed on the next block but fell, sliding upright in a seated position, the way good skaters fall. He tried again. Then again. And again, sliding off the block and spilling onto the ground. He looked displeased but patient.

New skaters joined the group. Some had their phones out to shoot video.

Ari stepped up onto the marble.

“You got that, Ar!”

He threw down, popped, flipped, landed clean and rolled away — off the block and past the fountain.

Skaters tapped the tails of their boards on the pavement, a universal sign of appreciation.

Jiro and Shiki gave their friend a moment to bask in the achievement, then went after him, convening in something of a hopping huddle, hitting one another on the head.

“That was the last try,” Mr. Rodriguez observed.