He's agile moving around the ring (6)
I believe the answer is:
goalie
'he's' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'agile moving around the ring' is the wordplay.
'moving' indicates anagramming the letters (letters are moved around).
'around' is an insertion indicator.
'the ring' becomes 'o' (letter resembling a ring).
'agile' with letters rearranged gives 'galie'.
'galie' going around 'o' is 'GOALIE'.
Can you help me to learn more?
(Other definitions for goalie that I've seen before include "Keeper (colloq.)" , "one saves" , "Soccer player who protects the target" , "Football player" , "number one" .)