The answer is generaly "Once".
When someone lashes out in anger its not something they can control. They need help. Until such time as they have had treatment they are definitly dangerous. I'd say "LEAVE NOW". Leave immediatly. Keep them at a distance until they have started treatment. At that time you should be fairly safe in public but DO NOT get close to them again until they have controlled their anger.
NOTE: It is not common for a person to be cured of this kind of behavior in a short period of time. Expect treatment to take years before they are cured enought to be around.

The reason I said "Once" is because some people turn the anger on themselves and only hit others by accident. They to need help with anger management but they are not a threat to you in the same way. They are generally unhappy with some aspect of themselves and, depending on the root cause, may be helped more by you being around.

If you have more detailed question I'd suggest either sending a PM to MrCuriousUSA or post here an I'll see if my wife can get you better help/contact info for local support groups.

Please remember, this kind of activity only gets worse.

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