Rating tennis badly and unwilling to compromise (12)
I believe the answer is:
intransigent
'unwilling to compromise' is the definition.
(intransigent means inflexible)
'rating tennis badly' is the wordplay.
'badly' is an anagram indicator.
'rating'+'tennis'='ratingtennis'
'ratingtennis' with letters rearranged gives 'INTRANSIGENT'.
'and' is the link.
(Other definitions for intransigent that I've seen before include "Uncompromising" , "becomes immovable" , "staying put" , "Not flexible" , "Not prepared to adapt or compromise" .)