USviewer: At a park in Berkeley, across the bay from San Francisco, protesters from both sides struck one another over the head with wooden sticks and Trump supporters fired pepper spray as police in riot gear stood at a distance.
Some in the pro-Trump crowd, holding American flags, faced off against black-clad opponents. An elderly Trump supporter was struck in the head and kicked on the ground.
Organizers of the so-called Spirit of America rallies in at least 28 the country's 50 states had said they expected smaller turn-outs than the huge crowds of anti-Trump protesters that clogged the streets of Washington and other cities the day after the Republican's inauguration on Jan. 20.
"There are a lot of angry groups protesting and we thought it was important to show our support," said Peter Boykin, president of Gays for Trump, who helped organize Saturday's rally in Washington.
In many towns and cities, the rallies did not draw more than a few hundred people. At some, supporters of the president were at risk of being outnumbered by small groups of anti-Trump protesters who gathered to shout against the rallies.
In Berkeley, the total crowd of both supporters and detractors numbered 200 to 300 people, police spokesman Byron White said. Three people were injured in the clash, including one who had teeth knocked out, and police made five arrests.
One Trump supporter who took part in the violence came equipped with a baton, a gas mask and a shield emblazoned with the American flag.
White said police did break up fights between the two sides.
"We've made a number of arrests, it's one of those things where we monitor the situation and take action as necessary," he said.
The violence comes a month after mask-wearing protesters at the University of California, Berkeley, shut down a planned speech by a provocative far-right commentator by lighting fires and smashing windows.
On Saturday, smaller skirmishes broke out in other parts of the country.
In Minnesota, 400 Trump supporters packed the state capitol rotunda in St. Paul and were met by a smaller group of counter-demonstrators, according to the Star Tribune. Scuffles erupted and six counter-protesters were arrested, the newspaper reported.
In Nashville, Tennessee, Trump supporters and counter-protesters cursed at each other and occasionally made physical contact, but state troopers broke up the fighting, according to the city's public radio station.
Most rallies appeared to take place without any disruption or violence, like one outside the Michigan State Capitol in Lansing.
"How can anyone be disappointed with bringing back jobs? And he promised he would secure our borders, and that's exactly what he's doing," said Meshawn Maddock, one of the organizers of the rally which drew about 200 people.
Brandon Blanchard, 24, among a small group of anti-Trump protesters, said he had come in support of immigrants, Muslims and transgender people, groups that have been negatively targeted by Trump's rhetoric and policies.
"I feel that every American that voted for Trump has been deceived," Blanchard said.
More than 200 supporters of the president rallied in downtown San Diego.
"After this, I think people will take the hint," said former U.S. Marine David Moore, 42, a participant in the rally. "It’s okay to voice support for the president and the country."
In Palm Beach, Florida, where Trump is staying this weekend at his Mar-a-Lago resort, the president's motorcade stopped and Trump stepped outside his car to wave at a crowd of dozens of supporters. A smaller group of protesters stood across the street.
In New York, about 200 people demonstrated their support for the president in front of Trump Tower in midtown Manhattan. In Washington, about 150 people marched from the Washington Monument to Lafayette Square in front of the White House to show their support for the president.