Jacks support becoming more insane (7)
I believe the answer is:
loopier
'more insane' is the definition.
('loopy' can be similar in meaning to 'insane')
'jacks support' is the wordplay.
'jacks' becomes 'loo' (I can't explain this - if you can you should give a lot more credence to this answer).
'support' becomes 'pier' (type of structure).
'loo'+'pier'='LOOPIER'
'becoming' acts as a link.
Can you help me to learn more?
(Other definitions for loopier that I've seen before include "More crazy" , "more unbalanced" , "Dafter" , "less stable" .)