Wears effeminate clothes below the belt (15)
I believe the answer is:
unsportsmanlike
'below the belt' is the definition.
'wears effeminate clothes' is the wordplay.
'wears' becomes 'sports'.
'effeminate' becomes 'unmanlike' ('unmanlike' can be similar in meaning to 'effeminate').
'clothes' indicates putting letters inside.
'sports' inserted inside 'unmanlike' is 'UNSPORTSMANLIKE'.
(Other definitions for unsportsmanlike that I've seen before include "Dirty" , "Like going for a trip when playing football" , "as most female athletes are essentially?" , "Sneaky" , "unfair" .)