A man was taken to hospital with a head injury after an assault at Mangerton on Monday.
Emergency services were called to a unit on Myuna Way after reports of an altercation just after midday.
A 20-year-old man was found with a head would. He had been struck with an object, Wollongong police said.
He was taken to Wollongong Hospital in a stable condition. His injuries are not considered life-threatening.
An 18-year-old man was later arrested at a home in Coniston and charged with special aggravated break and enter and commit serious indictable offence – wound.
He was refused bail to appear at Wollongong Local Court on Tuesday.
Police are looking to identify other people who may be able to assist with their inquires.