Well I'm off to Glastonbury Festival on Wednesday, as is my wont. A fantastic English cultural tradtion, like Appleby, though obviously not so old. I've never seen any horses drowned at Glastonbury, but people have been murdered, and assaulted in other ways. And there just occasionally happens to be a bit of rubbish too. If you cram a lot of people into a small place, things happen. Many wonderful things, and a small number of bad things.
Coincidentally, I have just been reading an account of attempts to ban Burslem Wakes in the Potteries in the 19th century, due to riotous behaviour. The arguments on both sides are reproduced pretty nearly verbatim in this thread more than a century on.