Rangers v Celtic
Scottish clubs Glasgow Celtic and Glasgow Rangers have been fierce competitors for more than a century.
But unlike most British cities, the footballing rivalry in Glasgow is often seen as sectarian.
Celtic have historically drawn support from the descendants of Irish Catholic immigrants.
Rangers meanwhile have traditionally found their support among Scotland's Protestant community.
Last season, rivalry appeared to escalate to a new level with confrontations on and off the pitch, and parcel bombs sent to the Celtic manager and prominent Celtic supporters.
The Scottish government has responded by drawing up new measures to tackle sectarianism related to football.
For Assignment, Rob Walker investigates the origins of the Old Firm rivalry and asks why the government's proposals are proving controversial.
Some listeners may find some of the sentiments expressed offensive.