Calvin Williams, the 52-year-old Cleveland police chief, showed up for a Thursday-morning news briefing wearing bike shorts. He normally wears a more formal uniform, with a white shirt and white hat, but on this day he was dressed entirely in black: Black sneakers, black socks, black shorts, and a black short-sleeve uniform shirt reading “Cleveland Police” on the back.

He carried a water bottle. It was going to be brutally hot, with protests once again likely to break out all over downtown. Williams has been doing much of his job on a bike, one of 300 purchased in advance of the Republican National Convention. And throughout this week, he's been ready to roll.

“Last day. Rounding third and heading home. We want to ask everybody to remain vigilant. … If you see something, say something,” Williams said.

Williams has been the cool head leading this week’s massive police presence in Cleveland. There are thousands of police officers and state troopers here, many from as far away as Florida, Texas and California. They come in every morning and leave every night by the busload. There are also federal law enforcement officials, including the Secret Service, which guards the Quicken Loans Arena and the convention center where the news media are headquartered.

But Williams has a vast area to supervise — the "event zone" that covers most of downtown. And he's been ubiquitous. At one point Wednesday, he was walking Fourth Street, a narrow, crowded artery leading to the arena, and people kept asking to pose with him for photographs, a request he obliged. But such congenial moments are constantly interrupted by protests — and Williams repeatedly has gone into the center of the scrums.

He's also tried to talk to protesters and cool down situations. At one point this week, specifically addressing the anarchists who wear masks, he said: "Come up and talk to me. You know, black guy in a white hat and a white shirt.”

He got slightly roughed up when he helped break up a skirmish Tuesday. The conspiracy theorist Alex Jones and fellow “patriots” became entangled with left-wing protesters in Public Square. Williams and fellow officers separated the two sides and escorted Jones out of the park. When a reporter later asked why he, the chief of police, would get in the middle of a fight, Williams sounded taken aback.

“If I’m out there and something’s happening, I don’t just stand by. I’m still a police officer," he said.

A few hours after the Jones incident, Williams again entered the fray when police chased a small cluster of anarchists who had been running through the streets, wearing masks or bandannas over their faces and alarming convention-goers. The chief told the protesters to disperse or face arrest. They retreated.

At a news conference the next day, a reporter asked Williams whether police had been given a workout by the anarchists.

“I think they got more of a workout than we did. They were on foot. Our guys were on bikes," Williams said.

He’s been the police chief for two and half years after 30 years on the force. A profile of Williams in 2014 by the Cleveland Plain Dealer described him as “pragmatic, cool and collected.” He has commanded the SWAT team, worked on the vice squad, been a liaison with the U.S. Marshals, commanded the city’s Third District and served as a deputy chief of field operations before taking the top job in February 2014.

The department has a troubled history. On Nov. 22, 2014, two officers shot and killed 12-year-old Tamir Rice while he was playing with a pellet gun in a Cleveland park. The officers were not indicted, but the city reached a $6 million settlement with the Rice family. A subsequent Justice Department investigation found a pattern of excessive force by Cleveland police, and the department is operating under federal supervision.

But this week, the Cleveland police have made a point of holding back for the most part. As of Thursday morning, the department reported only 23 arrests associated with the convention. Of those, 17 happened Wednesday afternoon, when protesters burned an American flag and, according to police, refused to disperse when ordered to do so.

Right in the thick of that chaotic scene was Chief Williams. He personally told protesters to leave, and said they'd be arrested if they didn't. He made good on his word.