(Reuters) - Twenty-two people have been arrested for throwing objects and setting off fireworks following Ajax Amsterdam's 2-1 Dutch cup semi-final win at Feyenoord on Wednesday, national broadcaster NOS reported on Thursday.
Ajax's Davy Klaassen suffered a head injury when he was hit by an object thrown from the stands, causing a lengthy delay as players from both teams walked off the pitch.
The match started five minutes late due to smoke from fireworks lit by Feyenoord supporters. It had to be stopped 21 seconds after kickoff to allow the heavy black smoke to clear.
Feyenoord said they decided to partially close a section of Feyenoord Stadium for the home match against AS Roma in the Europa League quarter-final on April 13.
Earlier it was decided that there will no away fans at both legs of the quarter-final, after a decision by UEFA followed the Italian authorities' ban on Dutch supporters.
The Dutch football association (KNVB) said it would introduce stricter measures on Thursday. The referee will automatically stop a match if objects are thrown onto the field from the stands or if a fan invades the pitch. If an object hits any player or the referee, the match will be terminated.
"With these steps, potential perpetrators will hopefully no longer dream of attacking the main players on the field. We're done with that," KNVB director of professional football Marianne van Leeuwen said.
"The field is sacred. The players and everyone else on the field must be able to do their job safely at all times."