A POLICE sergeant was bitten by a stray dog while chasing a bag snatcher in Yau Ma Tei yesterday. An old woman, 74-year-old Ms Chan Tai-ho, was ambushed by a 34-year-old man at about 10 am. The suspect allegedly snatched her wallet containing $160 at the staircase of a Shanghai Street building. He ran out and was immediately chased by the victim and two patrolling policemen who stopped the suspect in a back lane off Shanghai Street. During the struggle the police sergeant was bitten in the buttock by a stray dog at the scene.