A spat between a cyclist and a pedestrian took an unexpected turn Monday evening in Fremont when the pedestrian brandished a chainsaw, police said.

Police responded to the scene near the intersection of Stevenson Boulevard and Besco Drive in the Sundale neighborhood of Fremont about 6:20 p.m., according to the Fremont Police Department.

Once there they learned the victim, a Fremont resident, had been riding his bike south on the sidewalk on Besco Drive when he got into an argument with another man.

"The verbal altercation escalated when the suspect began chasing the bicyclist with a chainsaw in his hand threatening to harm him," police said in a statement.

The argument may have had to do with the cyclist riding under a fallen branch, according to Geneva Bosques, a spokeswoman for the Fremont Police Department.

"It sounds like the bicyclist rode under a tree branch that had either fallen or partially fallen on the sidewalk and the other man told him he was stupid for doing that," said Bosques. "The man had the chainsaw in his hand when it began and it escalated from there."

The cyclist was able to ride away from the situation. The investigation is ongoing and no arrests have been made.

Filipa Ioannou is an SFGATE staff writer. Email her at fioannou@sfchronicle.com and visit her on Twitter.