Complex sentence: In the 1921--22 season, the club achieved a clean sweep of all the domestic competitions they entered--the Irish League, Irish Cup, County Antrim Shield, Alhambra Cup, Belfast Charity Cup, Gold Cup and the City Cup.
Split into simpler sentences: In the 1921--22 season, the club achieved a clean sweep of all domestic trophies available to them. They won the Irish League, Irish Cup, County Antrim Shield, Alhambra Cup, Belfast Charity Cup, Gold Cup and the City Cup.