The former Prison Break star was arrested on 22 April (12), a day after police were called to Playboy Playmate Ashley Mattingly's Beverly Hills, California apartment amid reports of a bust-up.
He was placed on $50,000 (£31,000) bail and subsequently charged with the misdemeanour count, but, the star's lawyer, Harland Braun, has tirelessly protested his client's innocence, stating, "He was dog sitting on the third floor and as he was leaving he saw his ex-girlfriend in the lobby, and she became agitated and took his phone and threw it up against the wall. He basically wanted to get out of there, so he took her by the shoulders to sit her down on a chair. He didn't hit her."
And on Wednesday (23May12) Garrison pleaded not guilty, according to TMZ.com.
The misdemeanour carries a punishment of up to a year behind bars, but Garrison could find himself in further trouble if he is found to have violated his probation from his 2007 conviction for vehicular manslaughter and drunk driving. He was released from prison in 2009 after serving part of a 40-month sentence for the charges.
The actor, who is reportedly fronting acting classes behind bars, is due to be released on 29 June (12). A pre-trial hearing has been set for 11 July (12).