Northern Irish football suffered a major set-back in 1948, when supporters of Linfield invaded the pitch after a match against Belfast Celtic, attacking and seriously injuring three Celtic players. A historical rivalry between Linfield and Glentoran has escalated somewhat in recent years: there were riots in 2005 and on Boxing Day in 2008. In the 1970s, the political Troubles in Northern Ireland spilled onto the terraces of the football stadiums. This is seen as a major factor in Derry City leaving the Irish Football League to join the League of Ireland.