Is enthralled by bullet movement, describing projectiles (9)
I believe the answer is:
ballistic
'describing projectiles' is the definition.
'is enthralled by bullet movement' is the wordplay.
'enthralled by' is an insertion indicator ('enthral' can mean 'capture').
'bullet' becomes 'ball'.
'movement' becomes 'tic' (I have seen 'Nervous movement' mean 'tic' so perhaps 'movement' could also mean 'tic').
'ball'+'tic'='balltic'
'is' placed within 'balltic' is 'BALLISTIC'.
(Other definitions for ballistic that I've seen before include "Projectile" , "Moved by gravity" , "Like missiles" , "Relating to projectiles and their flight" , "Winsome deer" .)