After being kicked to the head, she lost consciousness and started fitting before Benjamin Riley, 41, called an ambulance, police say.

Mr Riley is facing trial in the Newcastle District before Judge Donna Woodburne after pleading not guilty to causing his then partner, Rebecca Radnidge, grievous bodily harm.

In his opening address, Crown prosecutor David Phillips described the couple's relationship in the lead-up to the incident as "rocky".

On the night of December 15, 2019, Miss Radnidge was talking to her mother on the phone about plans for Christmas. Mr Riley decided to take over the conversation and pushed her out of the conversation, Mr Phillips said.

During an argument over the call he struck her to the face, knocking her to the ground, the jury was told on Monday.

Enraged, he kicked her in the head while she was lying on the floor and offering no resistance, police say.

It is alleged that the blows to her head caused serious injuries including bleeding inside her skull and a compression fracture to her C7 vertebrae.

The bleeding on her brain caused her to lose consciousness and to start fitting. He tried to revive her by taking her into the shower, Mr Phillips said.

"At that point, realising the seriousness of the situation ... he called an ambulance," he said.

At John Hunter Hospital she underwent an emergency craniopathy, which involved opening her skull to remove blood and to reduce the pressure on her brain.

After a series of days in a coma she recovered to an extent but has sustained "a degree of brain injury", the jury was told.

When questioned by police the next day he said they'd argued, she she wouldn't let him leave the house, and he slapped her and she fell down. She became unwell and sick, she sat on the couch, he took her to the shower but her condition continued to deteriorate. He says it was at that point he called an ambulance.

Mr Riley has pleaded not guilty to inflicting grievous bodily harm with intent, and faces an alternative count of recklessly cause grievous bodily harm. The trial is continuing.

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