Girls went off occasionally muddy sport (9)
I believe the answer is:
wrestling
'sport' is the definition.
(wrestling is a kind of sport)
'girls went off' is the wordplay.
'off' indicates anagramming the letters.
'girls'+'went'='girlswent'
'girlswent' anagrammed gives 'WRESTLING'.
'occasionally muddy' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for wrestling that I've seen before include "Combat in ring" , "Ring sport" , "gripping contest" , "Hand-to-hand grappling" , "See 8" .)