Supporters of two of the four sides playing today at the Arena are reported to have clashed outside the Rocket Pub close to Coventry Railway Station hours before Ospreys game with Gloucester.
It was a bad afternoon for the Ospreys who were beaten 17-0 by Gloucester.
The second game which saw plenty of empty seats around the 32,500 capacity arena was won by Cardiff Blues 11-5 against Northampton Saints.