I once had one come at me. I made like a football punter adn put his sorry @$$ through the uprights. he came at me again and I let him have it again.
he found other things to do, and let me alone after that.
We use to have geese that would try to attack. You had to be pretty fast then grab them by the neck and avoid the wings and feet. They would usually go off really pissed off honking at you, lettin gyou kow that "you got off easy" If they keep coming, then grab and twist. Roast goose. I imagine you could do that with a swan but I am sure that they are considered a protected species.