Great success of small group setting leader back (4)
I believe the answer is:
riot
'great success' is the definition.
(thesaurus)
'of small group setting leader back' is the wordplay.
I cannot quite see how this works, but
'of' could be 'o' and 'o' is found within the answer.
The remaining letters 'rit' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
(Other definitions for riot that I've seen before include "Affray, fighting in the streets" , "Lavish display (of colour)" , "unrestrained revelry" , "Ruckus, insurrection" , "Public disorder" .)