Revolutionary rainproof clothing racket (4)
I believe the answer is:
scam
'racket' is the definition.
(I've seen this before)
'revolutionary rainproof clothing' is the wordplay.
'revolutionary' is a reversal indicator.
'rainproof clothing' becomes 'macs' (short for Macintoshes).
'macs' in reverse letter order is 'SCAM'.
(Other definitions for scam that I've seen before include "Swindle (Slang)" , "An informal swindle" , "rook" , "Con trick" , "Swindle (sl.)" .)