Hitting the horse AFTER you are out of harms way isnt protecting yourself. If a farrier has to hit a horse to keep him from getting to them that would be one thing, but hitting after they are out of harms way when the owner of the horse has already discussed not hitting the horse is unacceptable.
Relax - I actually agree.
I am just saying that I would never tell a farrier what they can/can't do as it is their neck they are risking. But what seems a vengeful whack after the incident would not be ok.
I wasn't there so I don't know the full story so don't want to speculate wether the farrier was right or wrong.