CTA No. 73 Bus Stop at Armitage and Hoyne. View Full Caption DNAinfo/Alisa Hauser

BUCKTOWN — Tempers flared on a CTA bus on Monday morning in Bucktown, when a woman struck another woman while arguing and then ran off, according to police and a CTA spokeswoman.

The 62-year-old victim on the No. 73 Armitage bus was hit in the head and face by an unknown woman, police said, and was treated for cuts and bruises on the scene in the 2100 block of West Armitage Avenue.

The woman's attacker ran away and was not in custody.

Witnesses saw the bus stop in front of a Starbucks at 2101 W. Armitage Ave. around 7:30 a.m and watched police climb aboard to help the victim.

The suspect was described as a black woman, about 5-foot-8 to 5-foot-9 inches tall, wearing a white shirt and blue jeans with a blue baseball hat with the word "Queen" in glitter, said Officer Michael Carroll, a Chicago Police Department spokesman.

Carroll said that the victim and her attacker did not know each other before the fight, but the victim was able to snap a photo of her attacker and give it to police.

Police and a CTA spokeswoman did not say what the fight was about.

A witness who was at a nearby Starbucks said he heard one of the baristas tell another person that the conflict may have been sparked "over someone FaceTiming too loudly."

Writing on a private Facebook page for Bucktown residents, the witness cautioned that he heard the information secondhand.