The sequence starts at 5:30 in the video. Rickson turns into the guys guard, then passes by going over the dudes head, lands in the 50/50 and finishes with an Achilles Lock. The camera work sucks during the pass and finish so I almost didn't see it. This video was back in the early 90's. Rolls studied Sambo as well as Wrestling, Judo... and passed what he knew down to Rickson. I'm sure they got the position from Sambo which has a more sophisticated leglock game.