The two top clubs were set to face off at the Johan Cruyff Arena on Sunday, but the game did not go ahead.
Angry fans were throwing flares onto the pitch during the game, with riot police on the scene as well.
Tear gas was involved at one stage of proceedings, with the game stopped at 11 minutes into the second half.
Feyenoord were winning the game 3-0 at that stage, which would have further upset the home fans.
Ajax are in dire straits at present, sitting 13th in the league with only a single win so far.