Officer Michael Brelo, the patrolman acquitted on Saturday, was one of several officers who fired a combined 137 shots at Timothy Russell and Malissa Williams in a car chase on Nov. 29, 2012. Police said they believed gunfire was coming from Mr. Russell’s car during the pursuit, but he and Ms. Williams were later found to be unarmed. Officer Brelo was singled out for the manslaughter charges because he climbed onto the hood after the pursuit ended and fired at least 15 rounds into the car, which prosecutors claimed was unjustified. In his acquittal, a judge ruled that Officer Brelo had feared for his life and that his actions were protected by law.

Though Cleveland’s population has a black majority, and though the mayor and the police chief are black, many African-Americans here say racial tensions and mistrust of law enforcement are common. Some speak of “two Clevelands” — a mostly white city with a bustling downtown and increased commercial development, and a mostly black one where schools are struggling and crime rates are high, and the police are not trusted.

That dichotomy was on display Saturday night as more than 100 protesters, many of them black, blocked traffic and chanted downtown about the verdict and broader perceived injustices. As the police followed the march, the protesters passed group after group of patrons dining outside at fashionable restaurants. Most of the diners were white, and many had come downtown for a Cleveland Indians baseball game. The protesters walked past many such places without incident, but at one point, the police said, a protester threw a sign at a restaurant patron. At other times, baseball fans loudly suggested that the protesters go home.

As the evening progressed and tensions rose, officers ordered demonstrators to leave. Most did not do so, and the police said 71 were arrested, many on charges of aggravated rioting and obstruction of justice.

“We only moved in to make arrests when things got violent and protesters refused to disperse,” Police Chief Calvin D. Williams said. “We want people to understand we’re going to help you in this process, but if things turn violent in this situation, we will take action.”