A bone-breaking attack on a Des Moines teenager believed to have been prompted by the color of his clothes "horrified" the boy's mother.

"I’m scared to let him go anywhere," said Christina Rumbaugh of Des Moines.

Jason Schlampp, 17, underwent a four-hour surgery for a broken arm at Iowa Lutheran Hospital, he told The Des Moines Register on Thursday. "I had to get 16 pins and two plates in my arm," he said.

Police have said that at about 1:40 p.m. Tuesday, Schlampp and a friend were leaving East High School to walk to the friend's house when they heard a group of four boys yelling at them. Schlampp and his friend kept walking, he told police.

Then, in an alley in the 800 block of East 15th Street, the four other boys confronted Schlampp and his friend, according to a police report.

Two of the boys said "F--- Bloods," and told Schlampp to get on his knees and apologize for wearing a red shirt, according to the report.

A police spokesman said that suggests the attack had something to do with gang membership.

Schlampp reportedly told the other boys that he would apologize, but he said he would not get on his knees.

"When we were in the alley, they hit me a couple times in the face, and they tried to get me to get on my knees and say sorry," Schlampp said.

"I said, 'I'm not going to get on my knees, but I will say sorry,'" he said. "They counted down from five and said, 'If you don't get on your knees then we'll beat you up again.'"

One of the boys "slammed" Schlampp to the ground, he said. He put his arms out to break his fall, and then broke his right arm.

No one has been arrested in the case. Rumbaugh and Schlampp said he isn't affiliated with any gangs, and Rumbaugh wants to know who assaulted her son.

"I wish we would find these kids," she said. "I don't want this to happen to any other kids."

Schlampp said he doesn't exactly know what to think after the assault, but he doesn't want anyone else to get hurt.

"I don't know what to think. My arm hurts, and ... I don't want it to happen to other students," he said.

Rumbaugh said her son has mostly been sleeping since he returned home from the hospital. She didn't let her other son, who also attends East High School, go to school right away after his brother was attacked, she said.

"He's a good kid, he didn’t deserve this," Rumbaugh said. "Someone needs to come forward with it that was there. His arm is never going to be the same."

The case remains under investigation by police.

Register reporter Linh Ta contributed to this story.