Police are appealing for anyone who saw an assault on a young male at a gig in the Ormeau embankment area of Belfast on June 19 to contact them.
It is understood to have happened at a gig by Dutch DJ Martin Garrix.
In a Facebook post, the PSNI say officers investigating this incident have this morning arrested a 20-year- old male in Belfast.
They say while "this young man is currently helping with our enquiries, we are still appealing for anyone who witnessed this incident, or who may have any information about it, to contact us on 101 quoting reference number 1438 of 21 June 2017. Alternatively, you can give information anonymously by contacting the independent charity Crimestoppers on 0800 555 111."