Johnson Sparkes, 29, of Dorset Avenue, Barry, appeared before Newport Crown Court where he changed his plea and admitted a charge of causing GBH without intent.
The offence relates to an incident on February 12, in which Sparkes unlawfully inflicted serious injuries on a woman.
A more serious charge of causing GBH with intent under Section 18 of the Offences Against the Person Act 1861 was not proceeded with after he entered a not guilty plea.
The charge was ordered to remain on file.
Following his guilty plea, Judge Matthew Porter-Bryant remanded Sparkes in custody pending sentence.
Bail was refused because of concerns including the likelihood of further offending, the risk of causing injury or fear of injury to an associated person, and the possibility of interference with witnesses or the course of justice.
The court also noted Sparkes was already in custody and had been recalled for a fixed period of 28 days.
Sentencing was adjourned to allow the court to deal with the case alongside a separate committal for sentence matter.
Sparkes is due to be sentenced on July 31.
He has previous convictions for violence.
