Boxer's first down in fight after agreement, most likely (2,5)
I believe the answer is:
no doubt
'most likely' is the definition.
(thesaurus)
'boxer's first down in fight after agreement' is the wordplay.
'boxer's first' becomes 'b' (ost letter of 'boxer').
'down in' is an insertion indicator.
'fight' becomes 'out' (I can't justify this - if you can you should give a lot more credence to this answer).
'after' is a charade indicator (letters next to each other).
'agreement' becomes 'nod' (a nod indicates agreement).
'b' put into 'out' is 'oubt'.
'oubt' after 'nod' is 'NO DOUBT'.
Can you help me to learn more?
(Other definitions for no doubt that I've seen before include "To be sure" , "Bound to, unquestionably" , "sign of agreement" , "Surely" , "Almost certainly" .)