What happens if a spectator is racist, abusive or damages property?

These are criminal offences under SASREA (s44(1)), each carrying a fine and/or up to 10 years' imprisonment:

• Anti-social behaviour (s44(1)(r)): engaging in delinquent and anti-social behaviour inside a stadium or venue, along a route or in its precincts, including racist, vulgar, inflammatory, intimidating or obscene language or behaviour.
• Damage (s44(1)(q)): damaging or destroying any movable or immovable property inside a stadium or venue or along a route or its precincts without authorisation.

Behaviour like this can also be the "historical behaviour" behind a spectator exclusion notice barring you from future events (s1, s22).