One on board, perhaps, or willing to participate (4)
I believe the answer is:
game
'willing to participate' is the definition.
(I've seen this in another clue)
'one on board perhaps' is the wordplay.
'one' becomes 'me' (a setter might use 'one' to humourously mean 'me').
'on' says to put letters next to each other.
'board perhaps' becomes 'ga' (I can't explain this - if you can you should believe this answer much more).
'me' after 'ga' is 'GAME'.
'or' is the link.
Can you help me to learn more?
(Other definitions for game that I've seen before include "What might get hung" , "meat from hunting" , "Sport - willing - lame" , "For instance, go" , "Competitive activity with rules" .)