Effects of a good wallop (7)
I believe the answer is:
clobber
This might be a double definition.
'effects of a good' is the first definition.
'clobber' can be an answer for 'effects' (clobber is a kind of effects). I'm not sure about the 'of a good' bit.
'wallop' is the second definition.
(thesaurus)
Can you help me to learn more?
(Other definitions for clobber that I've seen before include "Whitewash" , "Hit hard; clothing" , "Severely criticise" , "beat-up" , "belt or > sock" .)