One policeman and two fans were taken to hospital after being injured in clashes that took place during and after Saturday's game between arch-rivals Dinamo Zagreb and Hajduk Split.
Eighteen policemen were also among 36 people who sustained lesser injuries in the clashes. Dinamo clinched their fifth successive top-flight title after the 0-0 home draw with Hajduk.
Officers said 89 supporters were arrested and that seven police cars and several public transport vehicles were damaged.
"We will have to (introduce) drastic changes of laws. We need drastic measures against violent fans and swift implementation of those measures," Kosor said on a visit to the justice ministry.
"I'm very interested in the protection of (human) rights of those who attend soccer games, including policemen ... you saw footage of a father who was running away with his child. Just one hit with a broken seat could have had tragic consequences," she added.
Police said they were using videos to identify Saturday's main culprits.
The violent fans smashed seats before throwing them towards policemen and on to the running track around the pitch.
Croatia's football association has been fined regularly in recent years for the bad behaviour of fans, who have chanted racist abuse and clashed with police at home and abroad.
Despite pledges by the authorities to tame the violence with stricter measures, little progress has been achieved.
