He approached one of the young men who was talking with a friend and punched him in the head, grabbed him by the shoulder and continued punching him to the back of the head, causing the victim to fall to the ground.
Other party-goers intervened and police were called.
When police arrested Pratt he became abusive and threatening, telling senior constable Carey Williamson he would assault him, the summary states.
Attempting to handcuff Pratt he continued to resist police. When another officer arrived, he tried to get away and in doing so faced Constable Williamson.
As he "unleashed a torrent of abuse", Pratt arched his back and flung his head forward in a whip-like action, striking the constable in the face, left of his nose and upper lip, Sergeant Jodie Lawrence said.
"He headbutted the officer," she said.
Dragged outside, Pratt continued lashing out, kicking the constable in the back of the legs.
When spoken to by police, Pratt initially said the assault was self-defence, later stating "he didn't like that particular police officer as he didn't like the comments he made".
In another incident, on June 9, Pratt demanded to see his partner's cellphone, she became afraid of him and called police. Pratt then started yelling at the woman: "I am going to jail because of you b ..." and picked up a chair throwing it against a set of draws before punching her two or three times on the side of the face and pushing her onto the bed.
He also pleaded guilty to a charge of dangerous driving and being an unaccompanied learner driver.
On February 9, Pratt was clocked by police driving on Michael St, a 50km/h area at a speed of 122km/h.
While in police custody he damaged the sprinkler head activation system which resulted in two fire trucks being called to the station.
Judge Mill sentenced Pratt to 200 hours' community work and 12 months' intensive supervision on the two assault charges, disqualified him from driving for six months on the dangerous driving charge and ordered he pay reparation of $200 to the fire service.
The judge also remitted Pratt's fines and ordered he complete 80 hours of community work instead.
"This is your opportunity to put things right," the judge said in sentencing Pratt.