A trespasser is someone who enters onto land without invitation or implied permission.
Excessive force cannot be used to remove a trespasser as this is an assault. A better course of action is to call the police and later sue the trespasser for compensation for any damage caused.
In some situations it may be appropriate to apply for an intervention order to prevent a person from trespassing again [Intervention Orders (Prevention of Abuse) Act 2009 (SA) ss 6, 8].
The police can be called to remove trespassers who will not leave when told to or, who return within twenty four hours. The police can prosecute the trespasser who faces a penalty of up to $2500 fine and imprisonment for up to six months [Summary Offences Act 1953 (SA) s 17(a)].
A trespass can also be committed by causing an object to cross over onto a neighbouring property, for example, firing a gun at a cat on the neighbour's roof.
A neighbour who throws rubbish over a boundary commits an offence and is liable to a fine up to $750 [ Summary Offences Act 1953 (SA) s 57].
An uninvited person or gatecrasher at a party can also be guilty of trespass if they fail to leave when requested to do so (see Children and Young People)
An exception to the law of trespass is that an owner of goods is allowed to enter another's property to seize goods which are there through no fault of the owner of the goods. Reasonably necessary force may be used to reclaim the goods if the person took them wrongfully, or if that person knew someone else took them wrongfully [Huet v Lawrence(1948) QSR 168].
This does not allow a careless child to retrieve a ball that is there through the child's fault. Similarly a lender of goods cannot use force on the borrower to get the goods back, because the borrower did not acquire the goods wrongfully.