In England, perhaps because all Irishmen (each known as “Paddy”) have no love for the English, a paddywhack generally denotes a towering rage or, sometimes, the kind of thrashing that is most likely to accompany such a rage, a real, genuine, downright whacking.
But in America, where “Pat” or “Paddy” may be less given to fits of temper, the paddywhack has become considerably gentler.
It is still a punishment for a misdemeanor, usually one committed by a child, but it is rarely more than a spanking, often not very drastic.
Oh yes, for unfathomed reasons the ruddy duck is locally called paddywhack, often abridged to paddy.