undreds of protesters confronted State Police after last night's presidential debate in Dorchester, bursting through barricades and blocking roads as troopers in riot gear fought back with pepper spray and billy clubs.
At least 16 of the estimated 4,000 to 5,000 demonstrators who converged on the University of Massachusetts-Boston campus were arrested, State Police said, although only about 1,200 of them took part in the post-debate protests.
Soon after the debate ended at 10:30 p.m., a large group of protesters overturned a barricade and gathered on University Drive within sight of the debate venue, hurling fences into the roadway, State Police said.
The protesters - mostly supporters of Green Party candidate Ralph Nader, who was not allowed to participate in the debate - sat in the road, locked arms, and chanted as mounted State Troopers rode through the group, attempting to disperse them. Meanwhile, other troopers pleaded with the crowd to move off the roadway and allow about two dozen buses through to pick up those in the news media and the audience.
Soon afterward, the police abandoned their pleas, dragging at least 10 protesters over barriers and spraying others with pepper sray. Some officers also yanked metal barriers over protesters lying on the ground. At that point, some protesters began hurling stones, and one jumped onto a parked van and tore off the windshield wipers, flinging them toward the officers.
By 11:30, about 200 protesters remained, and State Police were encouraging a peaceful end to their demonstration, saying that all attendees had left UMass.
At 11:35, protesters started huddling in front of police officers, discussing whether they should demand the release of arrested protesters before heading home.
After 15 minutes of strategizing among protest leaders, Sean Nelson, 19, a Boston University student, secured officers' assurance that protesters would be released by 6 a.m. today, as long as they had no outstanding warrants. The protesters then dispersed.
The scene was in stark contrast to the circus-like atmosphere that prevailed earlier yesterday, as costumed demonstrators and placard-waving protesters made their way peacefully to the campus.
But soon after sundown, the trouble started. Prior to the debate, some of the arrests followed fistfights between rival political camps, State Police said.
Then, still more were arrested when groups of demonstrators tried, and occasionally succeeded, in knocking down barricades near the debate site, prompting State Police to pull out nightsticks and make arrests.
''They're shouting. I just saw another arrest made; it was someone trying to reach a barrier,'' State Police Captain Robert Bird said by telephone during one of the night's more volatile moments. ''It's as orderly as several thousand people behind a fence who don't want to be can be.''
Dominic Chavez, a Globe photographer covering the event, was injured when a demonstrator allegedly slammed him in the back with a camera. He was treated at Boston Medical Center. A few others were treated at the scene. A state trooper and his horse were also injured in scuffles with protesters.
One demonstrator, identified as Jonas Pool, 23, of Iowa, who said he traveled to Boston to support Nader, was standing in front of the barricade holding his hand aloft in a peace sign when several police officers tried to take him into custody.
Pool turned toward the crowd, which grabbed him, and a brief tug of war ensued. The crowd succeeded in pulling him back behind the barricade.
A short while later, about two dozen people stepped over the barricades and toward a squadron of State Police in riot gear, while holding their hands aloft in a peace sign.
For several minutes, it was a peaceful standoff. Then suddenly, the police rushed the protesters, swinging batons and spraying pepper spray into the crowd, forcing them behind the barricades. About 200 police nearby in riot gear mobilized and moved toward the crowd, which then backed off.
The tensions followed an incident-free day marked by nothing more severe than traffic jams.
At 5:30 p.m., the height of the rush hour, the Southeast Expressway, normally a clogged artery, was virtually deserted heading into the city. Apparently, all the warnings of driving chaos did not fall on deaf ears.
Not that all the hubbub didn't turn a few rubber necks as the day progressed. A contingent of motorcycle-riding troopers parked on the shoulder of Interstate 93 near South Bay shopping center attracted plenty of attention.
Three times, the troopers went from sideshow to main attraction, as they halted traffic on the expressway to allow unobstructed rides for the candidates' motorcades.
Near the University of Massachusetts at Boston campus, where debate preparations spiced up the normally placid landscape, many a driver slowed to gawk at the colorful contingent of protesters ambling down Morrissey Boulevard from the Red Line T stop.
''Their sheer numbers are disrupting traffic a little bit because they're spilling into Morrissey Boulevard,'' said Bird. ''But it's really been relatively quiet.''
Adding to the mix, about 7,000 people were converging on the Bayside Expo Center yesterday for Powersystems World, a computer convention planned 18 months ago - long before UMass was designated as a place for presidential fur to fly.
''I couldn't get into my hotel room'' Monday night, said Mel Elgar, who came to the convention from Ontario, Calif. ''They overbooked, and I didn't guarantee with a credit card for late arrival.''
Charlie Dec, a spokesman for the convention, said his organization sent its travel agents scrambling to secure entire blocks of hotel rooms when UMass was chosen as a debate site.
''We haven't turned anybody away because of hotel rooms,'' Dec said, ''but it wasn't easy.''
Those who left their cars at the curb with hopes of securing a taxi were in for a rude awakening.
''Every single cab except the ones that are broken down or have to get inspected is on the road,'' said Helen Kates, a longtime dispatcher for the Independent Taxi Operators Association.
Marcella Bombardieri, Patrick Healy, and Beth Daley of the Globe Staff contributed to this report.
