The pivotal phrase here is "genuine and reasonable apprehension". An inexperienced sailor will often have a genuine apprehension of collision that is not reasonable. He will take avoiding action earlier than necessary or when not necessary. He may take actions in panic that actually make things worse.
Yes. In the example that I am trying to describe. Starboard took actions that made things worse. It's usually comes with... I did not know what port was doing, therefore I must take action to avoid a collision. The actions make a collsion unavoidable.
In this collision example. I would expect the jury to find both at fault. Port for failing to stay clear of starboard and Starboard for changing course without giving port room and opportunity to stay clear.
Would this outcome be reasonable?
I think it's critical for people to understand that there is no burden of proof... Each side has to present evidence about the interaction on the water. Both could be at fault as the situation plays out.
I think many people are not quite on this page and want black and white answers 100% of the time.!
There is no get out of jail free card where Starboard can't stand up and say... i was on starboard... I took action I deemed necessary to avoid collision... I can't be at fault no matter what happens.
As always... communication helps enormously... but your expectation that the other guy will signal you his intention when you want does not allow you to pull the escape cord and hail protest or make the collision unavoidable if you don't get the communication.