Green’s Dictionary of Slang

to hit, to attack; also as n., a blow.

1892		H. Nisbet Bushranger’s Sweetheart 292: Ride them down, and blatter away at them.
1908		L. Doyle Ballygullion 202: Aways the barrel goes till it comes a blatter off the kitchen door that near shook it out av the jambs.
1925		L. Doyle Dear Ducks 181: If the old man hadn’t made smithereens of the milk-jug with the first blatter of the stick.
1933		M. Marshall Tramp-Royal on the Toby 252: A sudden blatter of hail.
1979		J. Morrow Confessions of Proinsias O’Toole 9: Them Prods are blatterin’ away like mad over there.
1981		S. McAughtry Belfast 44: What I’m thinking of doing right now [...] is to blatter away at the old Olivetti.