As he was being arrested, he struck the constable in the face with his head, then kicked him in the back of the legs.
His first victim suffered a cut to his left ear and swelling to the side of his head.
When spoken to by police, Pratt admitted the facts as outlined but claimed the initial assault was self defence.
In relation to the assault on the constable, he said he did not like comments the officer had made and he had smirked.
The driving charges related to a separate incident, in which Pratt drove at 122km/h in a 50km/h residential area, alone on a learner licence. The incident took place in Michael St, Masterton.
Pratt was stopped by police and arrested. He was on bail at the time and in breach of his curfew.
While in a Masterton Police Station cell, Pratt damaged a sprinkler head, activating the sprinkler system and fire alarm.
Defence lawyer Peter Stevens said Pratt did not have an extensive history of offending but did have some problems with his anger.
Judge Michael Behrens ordered a pre-sentence report, convicted and remanded Pratt until August 9.