Playing well, half-naked and relaxed (8)
I believe the answer is:
informal
'relaxed' is the definition.
(thesaurus)
'playing well half-naked' is the wordplay.
'playing well' becomes 'inform' (I've seen this before).
'naked' indicates the central letters.
The centre of 'half' is 'al'.
'inform'+'al'='INFORMAL'
'and' is the link.
(Other definitions for informal that I've seen before include "Casual or unofficial" , "Casual, not official" , "Casual, free and easy" , "Casual and unceremonious" , "Cosy -- loose" .)