BOULDER, Colorado (AP) — Police in Colorado are investigating a report that a woman punched a 12-year-old boy carrying a Donald Trump lawn sign because she was upset about his support for the president.

The incident was reported Monday in Boulder, a liberal city that is home to the University of Colorado. The boy, who was riding a bicycle, said a woman in her 20s or 30s rode a moped past him, saw the sign, then made a U-turn and “began assaulting him because of his political banner,” police said. They said she unsuccessfully tried to take the sign.

Citing a police report, KMGH-TV said the boy’s father gave police a statement about the alleged assault. The boy said the woman punched him in the back of the head and arms several times and caused a scratch on his left arm, according to the document.

The police records division previously released the full police report to other media but refused a request from The Associated Press for it Thursday because detectives have opened the case for further investigation. A police spokesperson did not return a telephone message seeking additional details.