Who knew there were violent gangs of young people in the early 19th century going to fairs for a punch-up? Here's a tale from Northumberland, the location of both Bellingham and Stagshaw Bank. This story is from 1881:

"Upwards of fifty years ago the old people used to relate how, in
their early days, young men from the districts beyond Bellingham
came to Stagshawbank in groups or clans for no other purpose
than to provoke a fight, which they never failed to do. When
the well understood battle cry of 'Tarset and Tarraburn, yet, yet,
yet!' resounded through the fair, then dogs and human beings
joined in a scene of wild confusion."

There's an account of the fair itself (but not the violence) from about 1850 here, if you're interested:

Corbridge Fair