Sport Dawson dominates (5)
I believe the answer is:
rules
'dominates' is the definition.
('rule' can be a synonym of 'dominate')
'sport dawson' is the wordplay.
'sport' becomes 'RU' (rugby union).
'dawson' becomes 'les' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'ru'+'les'='RULES'
Can you help me to learn more?
(Other definitions for rules that I've seen before include "strips" , "See 7" , "Is king" , "Australian football" , "instructions" .)