A Chicago police officer suffered a stab wound to the leg, Sunday, and three others were injured during a day of protests around the NATO summit.
Chicago police Supt. Garry McCarthy did not know what was used to stab the officer and became emotional when discussing the crowd with which his officers dealt.
"If you think it's easy to ask people to do what they did, it's not," he said, pausing to gain his composure. "Asking people to put themselves in harm's way, knowing that they're going to get assaulted, and to be able to stand there and take it, those guys were amazing."
Overall, officers arrested more than 45 individuals during a day of marches and protests that turned violent in the evening hours.
McCarthy commended his officers for showing "dramatic restraint" in the face of taunts and violence.
"I'm proud to be in charge of this department," he said.
The superintendent said his department was mostly prepared for the melee that erupted at 22nd and Michigan Avenue.
Officers knew that a group of Black Bloc anarchists planned to storm McCormick place after a group of war veterans finished its demonstration there.
McCarthy said officers used batons on the aggressive protesters because they were assaulted.
"They don't have to stand there and take an assault," he said. "Just because we've been telling you exactly what you were going to see for the last six months, it doesn't mean that you excuse it. The fingers should be pointed at the people who assaulted the cops."
The Twitter feed of Occupy Chicago was filled with differing sentiment. Many of the protesters and their supporters decried the brutality of the police officers and pointed to a lop-sided ratio of police to protesters.
Police stood by their use of force.
McCarthy said his department was tipped off that someone had assembled an improvised explosive device (IED) that was stored in a back pack near the demonstration at McCormick Place. Officers found a pack that contained an unknown liquid. The liquid was sent to a lab for testing.