Stroppy pros, to be sure, may be retrained (12)
I believe the answer is:
obstreperous
'stroppy' is the definition.
(obstreperous means stroppy or disobedient)
'pros to be sure may be retrained' is the wordplay.
'may be retrained' indicates an anagram (train can mean to shape or control).
'pros'+'to'+'be'+'sure'='prostobesure'
'prostobesure' anagrammed gives 'OBSTREPEROUS'.
(Other definitions for obstreperous that I've seen before include "Bolshie" , "Disruptive" , "Noisy, hard to control" , "Noisily defiant" , "Sober posture (anag) - unruly" .)