Police confiscated the bat, and he was then caught on camera clashing with counter-protesters.
A pro-President Donald Trump free speech rally drew several hundred to a plaza near City Hall more than a week after two Portland men were fatally stabbed trying to stop a man from shouting anti-Muslim insults at two teenage girls on a light-rail train.
Officers arrested four people from that crowd, but they released all others after checking people's identification.
Her son, Micah, was wounded as he and the others tried to intervene in what Portland police called "hate speech toward a variety of ethnicities and religions" directed at two women on the train.
What began as a tense exchange of name-calling and profane insults took a turn when counterdemonstrators began throwing glass bottles, bricks and balloons of "foul-smelling liquid" at officers, Portland Police said.
As of Sunday afternoon, about 500 people had said they would attend the event on Facebook.
Jeremy Christian, a 35-year-old with a prior felony record, was arrested and charged with murder in the May 26 attack, which Trump has condemned as "unacceptable" while saluting the three stabbing victims for "standing up to hate and intolerance".
The Patriot Prayer event, called The Trump Free Speech Rally, is being held at Terry D. Schrunk Plaza, which is federal property where guns are barred. They said they used "less-lethal chemical munition" such as tear gas to disperse the crowds.
The rally was organized by the conservative group Patriot Prayer, according to ABC affiliate KATU-TV, and scheduled before two men were allegedly killed by a man who police said shouted anti-Muslim slurs before stabbing them to death. To the west, in front of City Hall, protesters chanted and displayed signs with such messages as "Wake Up Portland!" Crowds have swelled to several thousand as demonstrators from varying groups have converged in downtown Portland.
Attendees included some of the biggest names on the so-called alt right, the loosely organized and mostly digital network of white nationalists, supremacists and other far-right activists which sprung to prominence amid President Donald Trump's rise to power. Kyle Chapman, the speaker for the planned event, told media earlier Sunday that it's good to see people "uniting under the banner of American nationalism". We need to stop spreading love to stop this hate.
Anti-Trump activists staged a separate demonstration in Portland on Saturday, as part of nationwide "March for Truth" rallies in support of investigations into Russian meddling in the 2016 presidential election and possible collusion by Trump's campaign.
Dozens of police officers in black protective gear and others on bicycles are in downtown Portland working to keep various groups separated.
Officers arrested at least 14 people and confiscated various weapons, including what appeared to be a knife, brass knuckles and a homemade slingshot.