May 25--TAMPA -- Thousands marched in downtown Chicago protesting war, heading toward a convention center where President Barack Obama hosted a NATO summit.

Police dressed in riot gear stopped them and asked the crowd to disperse. The majority of the protesters left; some did not.

Then violence broke out.

A group of Tampa law enforcement officers witnessed the whole thing. They attended the summit last weekend to compare how their security plans for the Republican National Convention compared with the Windy City's strategy for the summit.

The clash between police and protesters was eye-opening, said Hillsborough County sheriff's spokesman Larry McKinnon, who attended the summit.

The confrontation started when a group of what he called "anarchists" began taunting police.

"They were prepared to engage in conflict," McKinnon said. "They were wearing gas masks and they had their own medics. They had their own videographers."

McKinnon said officers asked the crowd to disperse at the end of the march. Those who stayed started provoking police, who were dressed in riot gear. When the stragglers wouldn't leave, officers tried to remove them by force.

Some protesters hurled sticks and bottles at officers, who responded with batons. Four officers were injured, including one who was stabbed in the leg, and 45 people were arrested.

Protesters in Chicago were prepared for a confrontation, but Tampa officers said that when the GOP convention comes to town, they'll be ready, too.

"We have the resources in place," McKinnon said