Resist getting extremely legitimate catch (6)
I believe the answer is:
buckle
'catch' is the definition.
(I've seen this before)
'resist getting extremely legitimate' is the wordplay.
'resist' becomes 'buck' (as in bucking a trend).
'getting' means one lot of letters go next to another.
'extremely' says to hollow out the word (remove centre letters) (only the extremes of the word are used).
'legitimate' with its middle taken out is 'le'.
'buck'+'le'='BUCKLE'
(Other definitions for buckle that I've seen before include "Bend out of shape" , "Fasten up - give way" , "Catch" , "(E.g. belt) fastener; crumple" , "Fastener on belt or shoe" .)