Section 418(2)(d) of the Crimes Act 1900 (NSW) refers to the use of force in self-defense, but this defense is not available if the person was resisting lawful arrest, even if they believed the arrest was unlawful. In your case, whether the police had lawful authority to enter the property, despite the implied consent being withdrawn through signage, could be relevant. If the police's entry was unlawful or excessive force was used during the arrest, Section 418 might provide a defense. Consulting a lawyer would clarify how it applies to the facts of your case.