Facts show boxing master's position (13)
I believe the answer is:
circumstances
'position' is the definition.
(thesaurus)
'facts show boxing master's' is the wordplay.
I cannot quite see how this works, but
'master's' could be 'ms' and 'ms' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for circumstances that I've seen before include "One's current state of financial or material welfare" , "Everything that happens to one in life!" , "Details" .)