Trickery disheartened school rowers (7)
I believe the answer is:
sleight
'trickery' is the definition.
(thesaurus)
'disheartened school rowers' is the wordplay.
'disheartened' means to remove the middle letters.
'rowers' becomes 'eight' (I've seen this before).
'school' with its middle removed is 'sl'.
'sl'+'eight'='SLEIGHT'
(Other definitions for sleight that I've seen before include "Dexterity (usually of hand)" , "It's deceiving to the eye" , "Artful trick" , "Trickery" , "Skilful deception" .)