Thirty three fans have been arrested, and five police officers hurt, when violence erupted after the Manchester United v Everton game on Saturday.
United won the match 2-0 at Goodison Park in Liverpool, but tempers flared outside the ground after the game.
Everton fans were angry that their former player Wayne Rooney now plays for United. And an Everton fan threw a coin at goalkeeper Roy Carroll.
Police called the violence a "large-scale disturbance".
Everton has said it will ban the fan for life who threw the coin at Carroll. Police also picked up a mobile phone from the pitch that was thrown.
Police said they would be looking at CCTV footage and talking to the Everton stewards about the attack. The FA is also involved.
One of the police officers who was injured needed treatment in hospital.