Mitchell Keith Robinson, 30, pleaded guilty on Tuesday in Brisbane District Court to five counts of assault occasioning bodily harm, serious assault on police, common assault and obstructing police.
Police were called to Northgate train station in Brisbane's northeast on November 28, 2021, after Robinson carried out a rapid series of indiscriminate attacks on passengers.
Judge Ian Dearden said CCTV footage of the assaults was "deeply disturbing and distressing".
Robinson could be seen walking through the carriage's aisle before punching a random passenger as they sat on a seat.
He then kicked the 11-month-old baby held in its mother's arms.
The mother was also assaulted before Robinson punched another person.
Further CCTV footage showed Robinson punching and grappling with people who intervened.
Bodycam footage showed Robinson refusing to exit from a police vehicle while kicking at officers.
Robinson was later placed in a medically induced coma due to drug-fuelled psychosis.
Crown prosecutor Brendan White said Robinson should be given a seven-year sentence to protect the community and police.
"It's truly a shocking thing to see footage of a powerful man delivering a kick to the head of an infant in its mother's arms," Mr White said.
A victim impact statement from one of the people Robinson assaulted said it had affected his sense of safety on public transport.
"If I can't drive somewhere, I can't go," the victim said.
Mr White said Robinson committed the assaults 20 days after being released on parole for a home invasion in which he pointed a firearm at police officers before being shot and wounded.
Defence barrister James Wallace said Robinson had shown genuine remorse.
"Those in prison became aware (his offences) involved a person aged over 60 and an infant, and that made him a target for assault in custody," Mr Wallace said.
The court was told Robinson had an offer of work on a dairy farm.
"He has no desire to take drugs again ... he does not want to be a danger to others," Mr Wallace said.
Mr Wallace said the injuries suffered by Robinson's victims were limited to "swelling, bruising and a little bit of bleeding".
Judge Dearden said Robinson had made the choice to use illegal drugs knowing they sent him into a paranoid and delusional state.
"You put people at extraordinary risk. It's lucky it was not worse," he said.
Judge Dearden said Robinson had turned people's lives upside down while they were just going about their business.
"There would be nothing more terrifying for a mother than having her child attacked while in her arms," he said.
Robinson was sentenced to four-and-a-half-years imprisonment and will be able to apply for parole immediately due to time served.
Judge Dearden told Robinson any drug relapse would be "catastrophic" for him.
"If you stuff it up once you get outside, you will go back," he said.
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