>>151258425
The boat that t-bones the other is on port and so needed to keep clear of the other boat on starboard (RRS 10). However the starboard boat could have potentially avoided the worst of the collision had they turned down, swinging their stern away from the port boat instead of turning up as they did.
These J-class yachts generally race with a 50m 'buffer' around them, iirc this collision happened at one of the few races where they didn't and then they went back to the buffer afterwards.