PORTLAND, Ore. – A man yelled about First Amendment rights on a MAX train Friday afternoon and assaulted a TriMet operator who asked him to leave, according to Portland police and TriMet officials.

The suspect, 23-year-old Steven Caldwell, was arrested on charges of assault, disorderly conduct, interfering with public transportation and interfering with a peace officer.

The alleged attack happened just after 2 p.m. on an eastbound blue-line train near Burnside Street and 102nd Avenue.

"He just started yelling and screaming, I'm not sure what he was mad about," said passenger Sabrina Hisey, who was riding the train to Gresham. "He started off by saying, 'everybody on the MAX,' and that honestly got everyone's attention, everyone was freaked out, because you know the stabbing happened last Friday."

The operator asked Caldwell to leave the train because he was being loud and disruptive, according to TriMet spokeswoman Roberta Altstadt.

Caldwell responded by pushing the operator down, Altstadt said.

"The MAX driver goes back to get him out and he beats the poop out of him," Hisey said. "He gets his head bashed in a few times."

Hisey said passengers pushed Caldwell off the train.

The operator had minor injuries. He was treated by medics at the scene, but did not go to a hospital, Burley said.

The incident occurred one week after a self-proclaimed nationalist allegedly yelled hate speech and stabbed three people on a MAX train. Two of the victims died.