Pittsburgh will import police from surrounding areas and cordon off the downtown area to ensure the G-20 summit will run smoothly.
Police experts say Gates probably overreacted. But Sergeant Crowley appeared to let the situation spiral out of control, they add.
The police union's combative press conference Friday was an example of how the profession closes ranks in times of trouble.
Arrests of those who challenge police authority are not uncommon, say civil libertarians.