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 "Type of Japanese wrestling", "Traditional Japanese wrestling by fat men", "Style of traditional Japanese wrestling", "A form of wrestling", "Form of wrestling", "Japanese form of wrestling", "Japanese wrestling for huge men", "Japanese wrestling with big fat men", "Jap. wrestling" and "Kind of wrestling".)