A teenager who beat his girlfriend's 79-year-old grandmother over the head with a sports trophy when she disturbed him burgling the family home was yesterday jailed for eight years. Recorder Michael Lunn delivered the sentence after a Court of First Instance jury found Lee Kin-wai, 17, guilty of robbery. The incident occurred when Madam Kong Wai returned to her family's Tsing Yi flat at 10.15am on September 14 last year. Mr Lunn said when Madam Kong tried to open the front door, she found it was chained from the inside. He said Madam Kong's neighbour cut the chain for her to enter the flat, when she was grabbed from behind in a neck hold and told to 'shut up or I will beat you to death'. When she tried to look at her assailant, she was pushed face down on a bed and beaten over the head with the trophy until she lost consciousness. A gold necklace and pendant were taken from her neck and $200 from her bag. The court heard the defendant was a boyfriend of Madam Kong's granddaughter, with whom she lived. The court also heard Madam Kong now has trouble seeing from her left eye and needs a walking stick.