Mad character after small crush (7)
I believe the answer is:
shatter
'crush' is the definition.
(thesaurus)
'mad character after small' is the wordplay.
'mad character' becomes 'hatter' (Alice In Wonderland).
'after' is a charade indicator (letters next to each other).
'small' becomes 's' (abbreviation - e.g. clothes size).
'hatter' after 's' is 'SHATTER'.
(Other definitions for shatter that I've seen before include "wreck" , "Ruin" , "Break into fragments" , "Completely upset" , "Go to pieces" .)