Brendan Darryl Girdler, 25, fronted the ACT Magistrates Court on Wednesday afternoon, having pleaded guilty to three charges including assault occasioning actual bodily harm.

Court documents show he was wearing only a pair of shorts when he approached a housemate as the man stood on the patio at their Macgregor home and chatted to his wife over the phone.

Girdler punched the man in the face, neck and torso "without warning or provocation" and in defiance of pleas to stop, with the victim desperately asking him: "What for, brother?"

Another housemate phoned emergency services after hearing "the sound of fighting" and walking outside to find "blood everywhere".

The victim, sporting a "displaced" nose and bruised left eye, later told police he felt scared during the December 2020 incident.

He said Girdler was "very angry" during the attack, which Special Magistrate Jane Campbell described as "bizarre" and "vicious" at a bail application in March.

Girdler was granted bail on that occasion, having spent 88 days in custody on remand.

He was due to be sentenced on Wednesday afternoon, but the court heard a pre-sentence report was yet to be completed because the 25-year-old had repeatedly failed to engage with the author.

Girdler's Legal Aid lawyer, Edward Chen, said such a report would "greatly assist the court" and claimed the 25-year-old had missed some appointments because his phone had been on "do not disturb" mode.

Mr Chen also said a forensic psychiatrist engaged to conduct an assessment of Girdler had, "for reasons unknown", not responded to recent attempts at contact.

Magistrate Glenn Theakston adjourned the sentencing until August 3, urging Girdler to do all in his power to have these things completed in the meantime.

Mr Theakston sought assurances from Girdler, who promised to attend the necessary appointments.

Prosecutor Vienna Conliffe had earlier indicated she would argue a term of full-time imprisonment was the appropriate penalty.

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