The sun shield is ridiculous - quite mad (6)
I believe the answer is:
insane
'quite mad' is the definition.
(I've seen this before)
'the sun shield is ridiculous' is the wordplay.
I cannot quite understand how this works, but
'sun' could be 's' (abbreviation) and 's' is present in the answer.
'ridiculous' could be 'inane' (both can mean silly) and 'inane' is found within the remaining letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for insane that I've seen before include "Round the bend" , "Demented" , "Mentally unhinged" , "Wild < cuckoo < cracked" , "nuts" .)