Betray Les wickedly to a boor (4,3)
I believe the answer is:
sell out
'betray' is the definition.
(I've seen this before)
'les wickedly to a boor' is the wordplay.
'wickedly' indicates anagramming the letters.
'to a boor' becomes 'lout' (I've seen this before).
'les' is an anagram of 'sel'.
'sel'+'lout'='SELL-OUT'
(Other definitions for sell out that I've seen before include "when they become famous?" , "Commercial success - total betrayal" , "When all tickets are booked in advance" , "Great commercial success, everything bought" , "Betray one's principles" .)