They (Amsterdam council) made a soccer based risk analysis, which was deemed low.

Then because of the current political climate they explicitly kicked it up to the counter terrorism bureau of the Netherlands to make a risk assessment. The NCTB said there where no credible threats or other direct indications of pre planned problems but did indicate the risk as above average, hence the local government had almost double the extra police they normally would have in the occasion of a soccer match.

Now an independent audit of the preparations is scheduled and a separate audit of the day itself.

As for what happened on the day itself, both groups are pointing at the other, and depending on the stance people have on Israël they blame a specific group.. but the fact is things are very unclear at this moment. We have very colored whiteness statements and videos that don't show whole incidents from prelude to finish, just snippets.

The police did indicate that because the people assaulting the soccer supporters using small groups and hit and run tactic, they had a lot of problems getting a handle on things, as usually soccer riots is 2 large groups duking it out.. this was very different.. another reason the police are also conducting their separate investigation as they need to learn lessons from this as well.

I'm inclined to deem both groups assholes and wait for the investigation. Regardless violence of any kind is unacceptable. And soccer matches should have a surcharge to pay for police presence as this should not be on the publics dime.

Yes they were expecting it. The mayor of Amsterdam said that there were about 800 extra police officers

They were expecting this but disregarded the most sensible option of canceling the match due to political optics