I could be wrong, but I believe the first thing you should do is speak with the site manager or event manager. Ask them to observe the fans in question. If the fans continue, the manager will take care of it. It is usually better to have them deal with it, for they have to power to remove fans without you having to penalize either team.

I do not know about resorting to a technical foul, a more experienced member will have to answer that.