Blackwood's Batter! (4)
I believe the answer is:
bash
This clue could be a double definition.
'blackwood's' is the first definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'batter' is the second definition.
(I know that batter can be written as bash)
(Other definitions for bash that I've seen before include "Social event - clobber" , "Dent - party" , "Strike hard; party" , "Shindig, function" , "Party - whack" .)