Arm and leg invested in this musical (8)
I believe the answer is:
harmonic
'this musical' is the definition.
(I've seen this before)
'arm and leg invested in' is the wordplay.
'and' is a charade indicator (letters next to each other).
'leg' becomes 'on' (cricket term, fielding positions).
'invested' becomes 'hic' (I can't justify this - if you can you should believe this answer much more).
'in' is an insertion indicator.
'arm'+'on'='armon'
'armon' inserted into 'hic' is 'HARMONIC'.
Can you help me to learn more?
(Other definitions for harmonic that I've seen before include "Related note - type of progression" , "I march on (anag)" , "Musical" , "Relating to pleasing note combinations" , "Note produced as an overtone" .)