As a hunt follower, Saggy, or were you a random bystander?
Either way, I hope you reported the miscreant with the knife/airhorn to the police, & I hope they threw the book at them. Were they prosecuted?
As an aside, I also, in my idealistic student days, went on a few anti- BNP marches.
We definitely used to attract the occasional oddball who was just out for a rumble. They were discouraged as best we could, & we didn't lose too many tears when they got themselves arrested for punching the nearest skinhead.
Their behaviour may have been unacceptable, & an embarrassment to the rest of us, but it didn't make the BNP any more loveable or racism any more excusable.
Equally, if the best you can do to defend hunting is 'but I've seen hunt protestors behave badly!' then I'm sorry, but I don't think it's enough.