2:59 PM PT -- Justin Arnold has broken his silence following the arrest ... owning up to the beer throw.
“I’m sorry to the Boston Celtics organization and TD garden for what I did," Arnold told WEEI. "It was unacceptable and I take full responsibility. I’ll never stop loving Boston”.
12:52 PM PT -- A spokesperson for the TD Garden tells TMZ Sports Arnold is now banned FOR LIFE for allegedly tossing the can onto the court.
"This act is a serious violation of our guest code of conduct," the spokesperson said.