A point of clarification. The song is called "Fenians of the Rock". It is about rioting by Catholic protesters objecting to the annual Orangemen's March held on the 12th of July. It isn't clear which year's disturbance is referenced. They are common but probably the 2009 riots in Glasgow and Dumbarton rather than Ireland.

The term "Fenians" here references the historic Fenian Brotherhood but is used simply to mean "Catholic activists" as is the term "Croppies" The term "Billy boys" and "Orangemen" is used to refer to members of the Orange Lodges, Protestant loyalists to the British crown, in historic reference to William of Orange.