Catalysis of the cleavage of rhamnogalacturonan, generating oligosaccharides of the form alpha-D-us-galacturonic acid-(1,2)-alpha-L-rhamnose-(1,4)-alpha-D-galacturonate-(1,2)-L-rhamnose-(1,2)-alpha-L-rhamnose-p-(1,4)-alpha-D-galacturonic acid, terminating at the non-reducing end with a hex-4-enopyranosyluronic acid residue.