No, Karl, and that is something that bugs me. At a recent event with big waves, coming to the line, I had a team that had already been stalled by a leeward boat begin sliding down the back of a wave; their sails were still on the starboard side of the boat, but they were moving backward at a knot or two, pumping rudders and yelling, and the wave had forced them past head-to-weather. We initially were set up to roll them close; we had speed and there was room. As soon as I saw them stall, I called for an aggressive duck, blew the jib and flattened out so the skipper had max visibility. As they fell down the back of the wave, our room to duck disappeared and we clipped their port stern with our starboard bow. I think if it had gone to the room, the decision would hinge on the position of the sail; the fact they were backing up wasn't the determining factor. Our defense would have been that we were not given room or opportunity to avoid; if we'd not tried to duck, we'd have had more substantial contact with their starboard hull as they were being forced onto a port tack. Our contact was certainly reduced by our ducking, but it spun them fully onto port tack and it left them feeling raped; even though we'd not been the team that forced them into irons, there were serious hard feelings on the beach because there had been contact.

The moral of the story; the rule references sail position. You can back up on the line without backing your sail. Overtaking boats had better watch out; RRS 21.3 will not save you.