Green’s Dictionary of Slang

bull n.2

also bull-calf
[Grose (1785) posits an eponym, one Obadiah Bull, ‘a blundering lawyer of London, who lived in the reign of Henry VII’: the OED rejects this as having ‘no foundation’. The link to Ireland is simply another example of derog. stereotyping; the term’s use predates any such link by many years. Note OF boul, boule, bole, fraud, deceit, trickery, ME bul, falsehood; NB ‘Sl. Terms & the Gypsy Tongue’ in Baily’s Mag. Nov. 1871 suggests origin in Hindi / Rom. bhul, a blunder]

[mid-17C–1940s] a blunder, an error; a self-contradictory proposition, esp. that which is made by an Irishman; thus bullery n.

In phrases

pull a bull (v.) (also make a bull)

[late 18C+] to blunder.