The former child star allegedly beat Michael Trujillo in the face with a splintered chair during a night of heavy drinking at his friend's Colorado home.
After concerned local residents called authorities, Bonsall was booked at the scene - only for cops to realise he had been wanted for more than a year after missing a court hearing in 2008.
He had allegedly violated terms of his probation stemming from an assault on his girlfriend in 2007.
Bonsall, best known for playing Michael J. Fox's little brother on the hit '80s sitcom, is currently being held in Boulder County Jail on $7,500 (£4,687) bail.
He faces up to six years behind bars if he is convicted of assault.