If it's being nasty about Napper Tandy, it's probably a sectarian song.
(By the way, Napper Tandy was one of the students at the Quaker boarding school in Ballitore in south Co Kildare, as was Edmund Burke.)
While bacach means lame as an adjective, it means a beggar as a noun. The tongue-twister "Ná bac le mac an bhacaigh is ní bhacfaidh mac an bhacaigh leat" means "Don't bother the beggarman's son and the beggarman's son won't lame you".
Napper Tandy was an okay guy, but the bourgeois didn't like him - he was an egalitarian small shopkeeper. Even though Napoleon had forced the British to release him, he supported the Haitian revolution, saying "we are all of the same family, black and white, the work of the same creator".