cats

My SO likes to go for walks, but there is a cat that constantly starts stalking towards them, hissing. Their grandmother has already been attacked by this cat, so I am looking for advice on the best thing to do in this situation. It's clearly an outdoor cat since it's well-groomed but we do not know the owner.

I am not familiar with cat behaviour, so I wanted to ask a community who was in order to get sound advice in a way that's safe for the cat and ourselves. Should I be using a spray bottle/water gun? Putting out smells the cat might not like? Any ideas on how to get it from constantly stalking and attacking people? Thank you.