Boy lost blood, but was exuberant (7)
I believe the answer is:
bubbled
'was exuberant' is the definition.
I can't judge whether this definition defines the answer.
'boy lost blood' is the wordplay.
'boy' becomes 'bub' (I can't justify this - if you can you should give a lot more credence to this answer).
'lost blood' becomes 'bled' ('bleed' can be a synonym of 'lose blood').
'bub'+'bled'='BUBBLED'
'but' is the link.
Can you help me to learn more?
(Another definition for bubbled that I've seen is " Effervesced".)