O'Callaghan. I don't know where the nickname came from, mate, but it was certainly apt with the 'quality' of his defending.
It must come from here: https://en.m.wikipedia.org/wiki/The_Brian_Conley_Show#"Dangerous_Brian"_Conley
Dangerous brian was a brian connolly character. A ***** stuntman. Became a name to associated to people prone to disasters
My memory of him was being told where to stand for a corner by the tarn fans away at Brentford. He duely nodded in the corner kick. He also used to gallop (slowly) rather than run. A bit like the knights in Monty python and the holy grail.