A man choked, stabbed and threatened to kill his stepmother while in a rage because Collingwood had lost a finals game.

The 33-year-old, who cannot be named to protect his victim, smashed his phone and punched items at home after watching Collingwood lose to the West Coast Eagles in the AFL qualifying final on September 8 last year.

He then went to his stepmother's St Albans house, let himself in and grabbed her around the throat, the County Court was told on Friday.

"Why are you going this?" the woman cried as she was dragged through the hallway to her bedroom and choked until she briefly lost consciousness.

"I'm going to kill you," her stepson said, according to prosecutor Robyn Harper.