Score badly with catholic sport (6)
I believe the answer is:
soccer
'sport' is the definition.
(soccer is a kind of sport)
'score badly with catholic' is the wordplay.
'badly with' indicates anagramming the letters.
'catholic' becomes 'c' (abbreviation as in RC for Roman Catholic).
'score' with its letters mixed up with 'c' gives 'SOCCER'.
(Other definitions for soccer that I've seen before include "Ball game" , "Football for Americans?" , "Association football" , "American football?" , "The beautiful game?" .)