We now know why former Broadway star Pia Zadora was arrested in Vegas over the weekend ... she allegedly tried to choke out her son ... TMZ has learned.
Zadora -- who famously appeared in the Academy Award disaster scene in "Naked Gun 33⅓" -- got into an argument Friday night with her 16-year-old son Jordan because he refused to go to bed at a timely hour.
Jordan told police he wanted to stay outside and talk to his stepbrother, so Zadora sprayed them with a hose to force them inside.
Jordan told cops his stepbrother tried to calm Pia down and she attacked him, punching him and scratching his face.
An hour or 2 passed, and -- according to the police report -- Jordan tried calling 911. He claims Pia tried to take his phone away, choking him in the process.
When cops arrived, they say everyone in the house -- Pia, her son and stepson, as well as her husband -- refused to come out to speak to them ... so SWAT formed a perimeter around the house.
Pia and her son Jordan eventually came out and spoke to police, and, according to the police report, Pia admitted she may have injured/scratched Jordan and her stepson during the scuffle ... but only by accident.