Game showing damaged boot in decline (8)
I believe the answer is:
football
'game' is the definition.
(I've seen this before)
'damaged boot in decline' is the wordplay.
'damaged' indicates an anagram.
'in' means one lot of letters goes inside another.
'decline' becomes 'fall' ('fall' can be a synonym of 'decline'**).
'boot' with letters rearranged gives 'ootb'.
'ootb' inserted within 'fall' is 'FOOTBALL'.
'showing' acts as a link.
(Other definitions for football that I've seen before include "Lob aloft (anag)" , "Loft a lob badly in this game" , "Ball game" , "Strange ballot of the game" , "See 20" .)