A club riot in retrospect — shambles! (8)
I believe the answer is:
abattoir
'shambles' is the definition.
(shambles could historically mean a slaughterhouse)
'a club riot in retrospect' is the wordplay.
'club' becomes 'bat' (as in sporting equipment).
'in retrospect' says the letters should be written in reverse.
'riot' back-to-front is 'toir'.
'a'+'bat'+'toir'='ABATTOIR'
(Other definitions for abattoir that I've seen before include "Make smile for camera" , "stunning location" , "building where blood is shed" , "place where animals die" , "Animal slaughter-house" .)