Enthusiastic about grasping right opening (5)
I believe the answer is:
intro
'opening' is the definition.
(short for introduction)
'enthusiastic about grasping right' is the wordplay.
'enthusiastic about' becomes 'into' (into can mean interested in or enthusiastic about).
'grasping' means one lot of letters goes inside another.
'right' becomes 'r' (common abbreviation).
'into' placed around 'r' is 'INTRO'.
(Other definitions for intro that I've seen before include "Launch" , "Instrumental part at start of song" , "Brief passage to start a piece of popular music" , "Opening notes" , "preface" .)