Sport, or cheating at it (6)
I believe the answer is:
diving
'sport' is the definition.
(I know that diving is a type of water sport)
'cheating at it' is the wordplay.
I cannot really see how this works, but
'at' could be 'in' (synonymous in some cases - eg at school, in school) and 'in' is located in the answer.
This explanation may well be incorrect...
'or' acts as a link.
Can you help me to learn more?
(Other definitions for diving that I've seen before include "Plunging into water - falling in the air" , "Throwing oneself into water" , "Going underwater" , "Plunging oneself into water" , "Plunging headlong" .)