Keen about being capped (4)
I believe the answer is:
knee
'keen about being capped' is the definition.
I can't tell whether this definition defines the answer.
'keen about' is the wordplay.
'about' is an anagram indicator.
'keen' anagrammed gives 'KNEE'.
Can you help me to learn more?
(Other definitions for knee that I've seen before include "Hinged joint" , "Joint of the body" , "Wounded in Indian Wars action" , "This is capped by the patella" , "Joint protected by the patella" .)