Brock of baseball (3)
I believe the answer is:
lou
'brock of baseball' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for lou that I've seen before include "Male or female" , "--- Costello, US comic" , "-- Reed, rock musician" , "man" , "-- Costello, Abbott's partner" .)