A guard at the troubled Banksia Hill Juvenile Detention Centre who was found guilty of assaulting a young inmate by grabbing him by the neck and slamming him backwards onto the ground had his appeal dismissed. Mark Thomas Griffen went on trial earlier this year charged with common assault of a 14-year-old boy after an altercation that was captured by CCTV in May 2022. The court at the time was told that after a morning at Children’s Court, during which the teen was disruptive, he was made to stand on an orange box to be searched with a hand-held metal detector. While surrounded by four guards, the boy hurled abuse at one of them — namely Griffen, who was a long-serving custodial officer — and then leaned into the 58-year-old’s space, prompting the latter to grab him and pull him down. The teenager, who has a history of spitting, punching, kicking and headbutting custodial staff, admitted he had verbally abused Griffen in the lead up to the incident and threatened to “king hit” him. While giving evidence at trial, the teen admitted he’d wanted to “scare Griffo”. In his testimony, Griffen said he acted out of self-defence, having believed the teen had a concealed weapon, and was about to assault him or spit on him. Griffen’s lawyers also argued that he had been authorised to act in the way he did and that he had applied a hold known as a “harness hold” or a “seatbelt hold” on the boy. But prosecutors alleged his actions were out of proportion with the perceived threat — a conclusion Magistrate Brian Mahon ultimately reached as well, ruling in May that Griffen had gone too far and fining him $3000. In appealing the decision, which saw Griffen be granted a spent conviction, lawyers argued that Mr Malone’s guilty verdict was unreasonable and could not be supported given the evidence at trial. But in his decision to dismiss the appeal on Friday, WA Supreme Court Justice Robert Mitchell found that Mr Mahon had delivered the correct verdict. He conceded that Griffen, who was aware of the boy’s violent history in relation to custodial officers, had been faced with “a difficult and challenging situation” on the day in question, “and was reasonably concerned that the complainant might have secreted an item that could be used as a weapon on his person”. “The complainant, who had in fact concealed such an item on his person, was not complying with the instruction to stand on the orange box to be searched,” court documents obtained by The West Australian state. “The complainant was making verbal threats and performed actions (shaking his arm free and ‘baulking’ at the appellant) that could reasonably be perceived as threatening a physical assault.” But Justice Mitchell said that rather than stepping back from the orange box or choosing another option that would have required a much lower degree of physical force, Griffen chose to grab the teen by the neck and slam him backwards onto the floor from the elevated height. “It was, in my view, more than the minimum degree of physical force required to control the behaviour of a 14-year-old boy of relatively small stature standing on a box surrounded by four custodial officers,” he said.