Sketch left, stuck on beam (7)
I believe the answer is:
portray
'sketch' is the definition.
(thesaurus)
'left stuck on beam' is the wordplay.
'left' becomes 'port' (left side of a ship - opposite of starboard).
'stuck on' is a charade indicator (letters next to each other).
'beam' becomes 'ray' ('ray' can be a synonym of 'beam'**).
'port'+'ray'='PORTRAY'
(Other definitions for portray that I've seen before include "Delineate" , "Depict, present" , "sketch" , "Play" , "Describe in words or make a picture" .)