American in favour of insurrection initially claiming disgraceful riot could be with stronger reason (1,8)
I believe the answer is:
a fortiori
'be with stronger reason' is the definition.
(I've seen this before)
'american in favour of insurrection initially claiming disgraceful riot' is the wordplay.
I cannot really understand how this works, but
'american' could be 'a' (common abbreviation - e.g. in organisation names) and 'a' is found within the answer.
'of' could be 'o' and 'o' is found within the answer.
an anagram of 'riot' is 'rtio' which is located in the answer.
This explanation may well be incorrect...
'could' acts as a link.
(Other definitions for a fortiori that I've seen before include "For stronger reasons" , "Latin phrase: With even stronger reason than that already accepted" , "By inference, even more" , "with greater reason" , "stronger premises" .)