Ursula Lindsey writes: At the edge of Tahrir Square on Tuesday night young men—and a few women—vied for a place in the front lines fighting the riot police, where, decked out in scarfs, goggles, and surgical masks, they formed a fearless rank.

When the protestors fell and were carried to the motorcycles and ambulances ready to spirit them to makeshift clinics and hospitals, others were ready to take their place.

The fiery confrontation taking place in Egypt today is about pushing the Army out of power. It’s also about teaching the police once and for all that the unchecked brutality it has long considered its privilege will no longer stand.

One might have though that lesson had been learned already. But “nothing has changed since the revolution,” says Mohammed Mahfouz, a former police officer. “The Ministry of Interior doesn’t respect the law, doesn’t respect human rights, doesn’t respect the dignity of citizens.”

The police force, which collapsed during the uprising against former Egyptian president and dictator Hosni Mubarak last January, “feel they’re in a feud against society,” says Mahfouz. “They have a desire for revenge.”

Police and protesters have clashed more or less continuously for the last four days. The police feel “not that they are enforcing the law but it’s a battle for their survival,” says Ihab Youssef, a former high-ranking officer in the Ministry of Interior who left the force to found an NGO dedicated to improving relations between citizens and the police.

The police’s use of excessive force in clearing a small encampment in the square Saturday morning is what led thousands of indignant Egyptians to come out into the streets in protest. The brutality that followed, with policemen aiming tear-gas canisters and rubber bullets at protesters’ heads and piling bodies on the curb like so much garbage, triggered the most violent confrontation and intense political crisis Egypt has witnessed since Mubarak’s ouster.