A jury trial began Thursday for a Denver police officer who struck a handcuffed 17-year-old boy three times after an arrest last year. Prosecutors say the officer, Dat Truong, 32, hit the boy out of anger and frustration after the teenager’s disrespectful “smack talking.” The officer’s defense attorney said the strikes were a legitimate use of police force aimed at curtailing the handcuffed boy’s threatening behavior. Truong is charged with a single misdemeanor count of harassment over the strikes.