Reward boy those people briefly upset (5)
I believe the answer is:
medal
'reward boy those' is the definition.
I can't tell whether this defines the answer.
'people briefly upset' is the wordplay.
'people' becomes 'men' (men are people).
'briefly' means to remove the last letter.
'upset' becomes 'dal' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'men' with its final letter taken off is 'me'.
'me'+'dal'='MEDAL'
Can you help me to learn more?
(Other definitions for medal that I've seen before include "Lamed by award" , "Winner's award" , "Decoration for a soldier perhaps" , "Commemorative piece of metal" , "eg VC" .)