John A, I completely agree that if a sailor breaks a rule and they know that they broke a  rule that they should take a penalty regardless of any hails of protest displays of red flags. The Basic Principle charges us to follow and enforce the rules including upon ourselves. Is the breach of a rule always clear to the sailor who may have broken a rule? Let's suppose that I tack in front of you from port to starboard. I believe that I completed my tack before you needed to change course to avoid. You disagree and hail "protest" (I am a dinghy sailor so I will leave the red flag out). I now have a decision to make. If I am sure that I completed my tack before you changed course, I may sail on. If it was close, I may take a penalty to avoid the "room". If your hail convinces me I broke rule 13, I take a penalty. 

There's not enough information in the diagram to infer that Yellow tacked too close (or more specifically, Green had to alter course to avoid Yellow while tacking).

What kind of boats are we talking about?  If you're talking about a 80 foot cruising monohull, or a slow tacking catamaran, perhaps it's too close.  Are we talking about a Laser or 470, both of which complete a tack in well less than a boat length?  Then very likely it’s not too close.

How fast were they going?  Also greatly impacts the answer.  If these are for example, Tech Dinghies, which both tack quickly and go very very slowly, it’s not anywhere near too close.  If we're talking 505s, 49ers, or A Cats, then Yellow was not only too close, but likely needs a trip behind the wood shed. If we're talking small modern keelboats, say a J80, it's likely still not too close. They do specify light air, so I suppose much is happening "slowly", but that makes which boats you're talking about even more important. You can tack a Laser in no wind in a boat length.  Try that in a Lightning. Whereas an A Cat can be going 11-12 knots in "light air" of 6-8 knots, so nothing in particularly "slowly".

The PC has to ask sufficient questions to determine the facts.  We don't have them here.  

My inclination, absent any other information, would be to say it's on Green to show that Yellow tacked too close.  I personally don't see that in the diagram.  Absent a good explanation, I wouldn't be able to find sufficient information to indicate Yellow tacked too close.

Why don't I see it? At point 2, Yellow appears to already be nearly head to wind, and Green is over 3 boat lengths away.  Most boats I can think of would be able to complete the last half of a tack in less than 2 boat lengths.  Unless they're very slow, or very slow to turn.  We can't really infer point "2.5" because they didn't draw it. We don't have that information.

So if I were on the PC, my questions would be around when Yellow crossed head to wind, and where Green was at that time. A couple of boat lengths is plenty of time to avoid a collision on virtually any boat.  Thus, I'd say the burden is on Green.  Whether Green saw them or not, also irrelevant.  That's a safety/seamanship question, not a rules question. If Green has a large Asym, and isn't keeping track of their fleet, leading to crash maneuvers, that's not a rules issue. It's a seamanship issue.

Generally, we're all bringing a lot of preconceived assumptions here based on the boats we have most experience with. But we don't have the information to see a rules violation in this diagram.

Bullseye. H12 hull with an aluminum marconi rig, cuddy cabin deck layout, half wishboom.

Ang, I think asking someone to do something, is probably ok, but the line is crossed when the protest chair starts 'statement taking' writing down what a witness says, taking possession of videos, and seeking out witnesses.

Nice work on the AI summary ;-)