Senga 2 is correct but it goes back much further than the 60s. Riots at Bridgeton cross in the east end were common even in the 20s and 30s. Murders were not uncommon and gangs of thousand would meet up at Glasgow Green and fight ,quite often to the death over the result of a Rangers / Celtic match.
When Rangers fan and gang leader Billy Fullarton died ,it was reported that over 140,000 attended the funeral.
It makes that English tribal nonsense in Germany look like
a punch up in a scone shop.