Playing scales, or a game (8)
I believe the answer is:
lacrosse
'a game' is the definition.
(lacrosse is a sport)
'playing scales or' is the wordplay.
'playing' is an anagram indicator.
'scales'+'or'='scalesor'
'scalesor' with letters rearranged gives 'LACROSSE'.
(Other definitions for lacrosse that I've seen before include "Ball game using netted stick" , "Game played with netted sticks" , "Sport played with sticks" , "Score's uncertain after the Spanish" , "Like thirteen of the other clues in the French" .)