Almost certainly agree the bout was rigged (2,5)
I believe the answer is:
no doubt
'almost certainly' is the definition.
(I've seen this before)
'agree the bout was rigged' is the wordplay.
I cannot really see how this works, but
'agree' could be 'nod' (I've seen this before) and 'nod' is found within the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for no doubt that I've seen before include "Bound to, unquestionably" , "Surely" , "Almost certainly" , "To be sure" , "sign of agreement" .)