Some Angevin troops opening passage (5)
I believe the answer is:
'opening passage' is the definition.
(I've seen this before)
'some angevin troops' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'INTRO' is hidden within 'angevin troops'.
(Other definitions for intro that I've seen before include "Opening notes" , "Instrumental part at start of song" , "Jazz piece" , "Musical opening" , "Early music piece" .)