An Adelaide medical researcher on his way to monitor animals testing a new vaccine was carjacked by an American baseballer on LSD and in the midst of a “bad trip”, a court has heard.

Timothy William Cusick, of San Francisco, pushed Dr Austen Chen out of his car on North Terrace about 1.50am on March 20, before crashing the vehicle into a tree at nearby Richmond.

The 28-year-old had been in Adelaide playing baseball for Henley and Grange Baseball Club at the time and has been required to remain in Australia since his arrest.

His parents travelled from the US to be at today’s hearing, when Dr Chen told the court his team had spent “years of hard work” developing a new vaccine.

“It has now entered a crucial stage of being tested on animals, which means I have to constantly come to check animals during the early mornings,” he said in a victim impact statement read by prosecutor Georgina Nicholson.

“It’s impossible for me to avoid doing this, otherwise we would never get scientifically valid results.”

He said the incident has profoundly affected him and he has no option but to continue his early morning shift.

“I know I am not 100 per cent OK … the anxiety and fear will be forever with me unless I stop doing it,” he said.

Marie Shaw, for Cusick, said earlier on the night of the carjacking her client had met up with a woman, drunk whisky and had taken LSD.

She said he was in the midst of a “bad trip” at the time of the incident and was trying to get to the airport to return to America because he believed he was being chased and his life was under threat.

Reading a letter to the court, Cusick, who will likely be deported at the end of his sentence, offered his “deepest apologies” to Dr Chen.

“It pained me to read of the damage that I caused you and your family and it makes me sick knowing that it was me that put you through it,” he said.

“Not a day goes by when I don’t think about what I’ve done and the effect that it must have had, and continues to have, on those involved.”

Ms Shaw urged Judge Joanne Tracey to consider a suspended sentence, but Ms Nicholson called for immediate jail time.

“This is a very bizarre and very unfortunate case, there’s no denying that,” Ms Nicholson said.

Cusick, who helped launch a baseball bat company in 2017, has pleaded guilty to committing theft using force and driving at a dangerous speed.

Judge Tracey continued his bail ahead of sentencing later this month.

AAP