Resist before the French collapse (6)
I believe the answer is:
buckle
'collapse' is the definition.
(buckling is a kind of collapsing)
'resist before the french' is the wordplay.
'resist' becomes 'buck' (I've seen this before).
'before' means one lot of letters go next to another.
'the french' becomes 'le'.
'buck'+'le'='BUCKLE'
(Other definitions for buckle that I've seen before include "Catch" , "Shoe or belt fastening" , "Collapse under pressure" , "Crumple under pressure, like shoe clasp" , "(E.g. belt) fastener; crumple" .)