Manning and his teammates left the subway wearing hats and scarves provided by Joyner, who said she was worried about students' welfare on a day when the temperature was in the single digits.
Police say one of the students "caught the attention" of officers stationed near the subway stop. As officers approached, the group scattered.
A surveillance video shows children running down Girard toward 15th Street, Manning among them. A police wagon - transporting a homeless man to a hospital, Ramsey said - pulls up as the group runs.
Since the surveillance footage was taken from a street camera that switches angles every 10 seconds, it is difficult to tell exactly what happened during Manning's arrest.
But one segment of the video shows Manning walking around the side of the wagon, where an officer appears to push him up against the vehicle.
Later, Manning can be seen on the ground in what Ramsey called a struggle with officers. Several police cars, lights flashing, idle nearby. In another segment, he is standing, surrounded by officers.
Lewis Small, Manning's attorney, said that after his client's arrest, a female officer grabbed the teen's genitals during a pat-down search and pulled, causing a testicle to rupture. Joyner said Manning underwent emergency surgery the next day and may have been rendered sterile.
"It's horrible. It's sexual assault, as far as I'm concerned," Small said.
Joyner called Manning a straight A-student, and Ramsey said he had no criminal history.
Ramsey said he was unsure how Manning's injury had occurred, although an officer visible in the security footage has been placed on desk duty. It is unclear whether that officer searched Manning, Ramsey said.
Manning has been charged with three misdemeanors: reckless endangerment of another person, simple assault, and resisting arrest. Small called the charges outrageous.
Ramsey said Internal Affairs investigators would like to speak to Manning. Small said he would not let Manning speak with police until the charges are dropped.
"I'm not going to allow my client to sit down and give a written statement. That's in effect malpractice by any attorney while criminal charges are outstanding," he said.
Ramsey said the department was taking the incident "very seriously," and asked any potential witnesses to come forward with information.
"We want to piece together what happened," he said.