Excluded from national team perhaps, though never bettered (8)
I believe the answer is:
uncapped
'excluded' is the definition.
The answer and definition are not the same part of speech. However, past participle verbs and adjectives can occasionally define each other.
'from national team perhaps though never bettered' is the wordplay.
I cannot really see how this works, but
'from' could be 'un' (I've seen this in other clues) and 'un' is found in the answer.
'bettered' could be 'capped' (I've seen this in another clue) and 'capped' is found in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Another definition for uncapped that I've seen is " Having no upper limit".)