I have guards with a custom faction.
In the Interfaction Relations I gave this faction a -100 disposition towards the PlayerFaction. They also have Aggression of 100 and Responsibility of 5.

But all they do is shout insults at the player, I need them to attack the player on sight, just the player, not any of the other NPCs.

Any ideas on how to do this?

Thanks.

I'm guessing they're tagged as guards in order to be able to arrest and add bounty to the player, but that might also affect their combat if you're "not guilty". If you want them to attack instead of arrest, then removing it (which may mean changing their class from a built-in one) could be the answer.

Do these guards have any other factions assigned that the player might be interacting with?