What's spent on Wall Street banks in large-scale collapse (6)
I believe the answer is:
buckle
'collapse' is the definition.
(buckling is a kind of collapsing)
'what's spent on wall street banks in large-scale' is the wordplay.
'what's spent on wall street' becomes 'buck' (I can't explain this - if you can you should give a lot more credence to this answer).
'banks in' means to remove the middle letters (the edges or banks of the word).
'large-scale' becomes 'large' (similar in meaning).
'large' with its middle removed is 'le'.
'buck'+'le'='BUCKLE'
Can you help me to learn more?
(Other definitions for buckle that I've seen before include "Shoe or belt fastening" , "Give way to pressure" , "(E.g. belt) fastener; crumple" , "Fastener on belt or shoe" , "Bend - warp" .)