My wife and I had that happen to us at Saba Rock. The two of us were on a Moorings 37. It was about three hours after dark when a large power cat, about 47 or 48 feet tied up to a mooring ball on their starboard hull only. Of course they were moving back and forth and coming close to hitting us. We didn't know this as we had already gone to bed and they woke us up yelling. I got up and went topside, I couldn't believe what I saw and then the lady skipper informed me I was going to have to move! There were at least 8 of them aboard and they were intentionally acting like they were trying to intimidate me. I told them I was here first and I had my mooring ball receipt and I wasn't going anywhere. I didn't mention her sloppy seamanship. They started acting like they might attempt to board our vessel. I didn't do or say anything more. I may be getting old, but my wife standing on the companion-way ladder next to the galley, had they attempted to board, I would have asked my wife to hand me the large butcher knife. Although this old former Marine prefers on old fashioned K-bar. We were there first!