Club act has change of heart: he's involved in scam (9)
I believe the answer is:
truncheon
'club' is the definition.
(truncheon is a kind of club)
'act has change of heart he's involved in scam' is the wordplay.
I cannot quite see how this works, but
'act' could be 'run' (run is a kind of act) and 'run' is found within the answer.
'of' could be 'o' and 'o' is present in the answer.
'heart' could be 'h' (card game abbreviation) and 'h' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for truncheon that I've seen before include "Cosh" , "Police weapon" , "Police staff" , "Peelers' baton" , "Police baton" .)