The former child star, who played Michael J. Fox's little brother on the hit '80s sitcom, is said to have hit Michael Trujillo in the face with a splintered bar stool during a night of heavy drinking at his friend's Colorado home.
Concerned neighbours alerted authorities, who booked the 28 year old at the scene despite his claims he had no recollection of the brawl, according to the Colorado Daily.
A police report obtained by the publication reads, "Bonsall said that he and Trujillo both are bipolar and like drugs. Bonsall said that he takes a lot of drugs and sometimes those drugs make him forget things."
Officials then discovered Bonsall has been wanted since July 2008 after he failed to appear at a hearing for allegedly violating his probation, linked to a 2007 assault charge.
He is currently behind bars at Boulder County Jail.