Amount of money offered initially for wrestling (4)
I believe the answer is:
Here is my best explanation:
'wrestling' is the definition.
'amount of money offered initially' is the subsidiary indication.
'amount of money' becomes 'sum' ('sum' can be a synonym of 'amount of money'**).
'initially' indicates taking the first letters.
The initial letter of 'offered' is 'o'.
'for' is the link.
(Other definitions for sumo that I've seen before include "Japanese wrestling with big fat men", "A form of wrestling", "Traditional Japanese wrestling by fat men", "Type of Japanese wrestling", "Japanese wrestling for huge men", "Large Japanese wrestler", "Japanese form of wrestling", "Jap. wrestling", "Kind of wrestling" and "Form of wrestling".)