That's a question I have never fully understood but ...

Firstly if it charges and you can't escape, it gets shot!

Like the one the faced me off in an angry but perhaps inquisitve manner.

Also as said in the story the stations don't always use all of their leasehold. The cattle outside the the fenced area aren't usually mustered. Sometimes trusted hunters can hunt these areas pretty much at will.

As Matt says, a grumpy old bull with a full set of horns will probably be a scrubbie.

The absence of ear tags is another sign.

Plus some areas, such as Aboriginal Lands may not run cattle anyway, so all the cattle there are scrub feral cattle.

We were told there was no scrub bull shooting, which was a pity. But I think you would have to be a trusted person to be given this right within the fenced areas. Perhaps had I known, I would have asked can we hunt scrub bulls in the unfenced areas.