Infantryman under command is pleased (8)
I believe the answer is:
gruntled
'pleased' is the definition.
The definition and answer can be both to do with human feelings as well as being past participle verbs.
Perhaps there's an association between them I don't understand?
'infantryman under command' is the wordplay.
'infantryman' becomes 'grunt' (I've seen this in another clue).
'under command' becomes 'led' (I can't explain this - if you can you should give a lot more credence to this answer).
'grunt'+'led'='GRUNTLED'
'is' acts as a link.
Can you help me to learn more?
(Another definition for gruntled that I've seen is " Happy".)