A Nottingham Forest fan who allegedly threw a smoke bomb during the match against Derby on Sunday is among four people arrested for trouble at the game.
A police spokesman said one Forest fan threw a smoke bomb into the Derby fans area.
Another supporter at the stadium was arrested for pitch encroachment, and two for affray. A police spokesman said the arrests were a mixture of Derby and Nottingham Forest fans.
Seven fans had to be kicked out of the ground by security staff.