Player willing to run (5)
I believe the answer is:
gamer
'player' is the definition.
(I've seen this before)
'willing to run' is the wordplay.
'willing' becomes 'game' (game can mean willing to do something).
'to run' becomes 'r' (cricket abbreviation).
'game'+'r'='GAMER'
(Other definitions for gamer that I've seen before include "More spirited" , "One plays" , "I bet" , "One role-playing on computer" , "More handicapped" .)