Police arrested six people from Sheffield after the Blades' play-off defeat against Wolves at the Millennium Stadium in Cardiff on Monday. A total of 18 arrests were made after the match, which saw Sheffield United lose by three goals and miss out on promotion to the Premiership.
South Wales Police said there was no repeat of the trouble that happened in Bristol and Weston-super-Mare on Sunday in the run-up to the game when rival fans clashed.
But officers are now checking CCTV tapes of the trouble in the Bristol area in a bid to identify the ringleaders of what they believe was orchestrated violence.
In Weston-super-Mare about 100 Sheffield United and Wolves supporters were involved in several disturbances between 1600 and 1700 BST on Sunday.