Four Cardiff City fans were arrested for "alleged racially aggravated abuse" during Saturday's 1-1 FA Cup draw at Reading, Thames Valley Police said.
The four males have been released under investigation.
Two of the four, aged 15 and 24, are from Caerphilly, with a 16-year-old from Abergavenny and a 21-year-old from Crickhowell arrested too.
Thames Valley Police said: "The force will continue to work in partnership with the clubs and South Wales Police."
Warnings relating to the alleged incidents were issued via the public address system at Madejski Stadium.
On Saturday, Cardiff City said in a statement they were aware of the allegations.
"We will be speaking with Reading Football Club, Thames Valley Police and South Wales Police - in attendance with our travelling support - to ascertain the facts of the matter," said the Bluebirds.
"We will conduct these conversations with the relevant authorities before making any further comment."
A Football Association spokesperson said the body is aware of the allegations and will also be investigating.