This is an excellent question.  I’ll open with case 50, or “Port shall not scare Starboard”

How about Case 118? "Room is room"

Case 88 - "A boat may avoid contact and yet fail to keep clear."

 Cases/Appeals groupings ...

Case 75,  Case 118 and US20: a study of sailing in/out of mark-room

US122, US124, US125: a study in on the water protest requirements

Case 14: When rule 17 applies between boats, the windward boat must keep clear of leeward ... even if she thinks leeward is sailing above her proper course, Windward's only option is to protest Leeward.  Windward can't refuse to sail higher if she disagrees with leeward.  RRS 17 does not provide room to windward and thus no access to rule 43 exoneration for breaking rule 11

146 Definitions, Room 
Rule 11, On the Same Tack, Overlapped 
Rule 16.1, Changing Course 
Part 2, Section C Preamble 
Rule 43.1(a), Exoneration 
Rule 43.1(b), Exoneration

Barging and when it's too late to luff the windward vessel.

Good one for new racers

Ric re:"Port shall not scare Starboard"

Imagine doing a reverse replacement in the next horror movie ...

"John, don't go into that dark abandoned mortuary ... I'm very reasonably apprehensive". 

:-)

Case 138 is fundamental to preserving the ethos of our sport. It gives examples of Misconduct. 
One example that deserves to be enforced more frequently is 'acting recklessly or in a manner that does, or is likely to, cause damage or injury'.

Thanks, everyone.  I'll review those.

Case 141 for definitions regarding damage.

Hi Vincent

I have found the World Sailing App to be a must have. It is a full copy of the RRS. It has an Integrated ebook version where it collates the RRS the World Cases and the Equipment Rules of Sailing. With this version you can select any rule and get a list of all the cases attributed to that rule. You can then see a summary of the case with an option to read the full text of the case together with any diagrams applicable. 

There is a charge for the Integrated eBook.  Approx $US 14. However a must have. 

Here’s a link to Apple App Store 

 https://apps.apple.com/au/app/world-sailing-2021-2024/id1152317815    

Thanks, Paddy.  I've just been using downloads of the rules docs and cases on my computer and phone so far, but I'd admit that I don't really appreciate what additional facility the app might provide.  I'll try it.  Everybody and his brother wants you to download their app these days, so my default has become not do do so.  I'm sure I'm missing out on some good stuff.
-Vince

Hi Vincent
Thanks for your reply and I get it about buying apps. I just think the convenience of having links to all the cases was much easier than doing all the searching and collating myself. Suppose it’s what you get used to. 
Anyway good luck with your venture into the world of judging
P

Way back in 2010, Jos Spykerman ran a series of blog posts called Pillowcases

http://rrsstudy.blogspot.com/p/pillowcasebook.html

He called them 'pillowcases' because the cases make good bedtime reading for judges <g>.  You'll have to read Cases 114 onwards for yourself because they came out after 2010.

You don't know what you need to know in a case until you've read the case.

As you are no doubt aware, Part 1 of the case book is arranged in RRS order, with the headnotes of the relevant cases, just like the hotlinks in the Rules section of racingrulesofsailing.org, so you can easily see all the cases applicable to each rule.  Part 2 of the Case Book has the cases themselves, in chronological order.  The RYA Appeals Book has a particularly easy to use matrix of rules and cases and appeals, and the US Sailing Appeals Book has a very nice collation of Appeal diagrams:  I find the diagrams more memorable than the words.

Some cases form pairs, dealing with two options or extremes of similar situations.  Matching these up can be very helpful.

Here are what I think are roughly the 'leading cases'.

Right of Way: Case 50, Case 88, 

Room:  Case 21, Case 103, Case 114, Case 118.

Difference between Right of Way and Room:  Case 75, Case 101

No need to anticipate:  Case 27, Case 53, Case 87

Contact ROW boat can avoid (pair):  Case 123, ROW boat cannot avoid:  Case 87

Contact, Intentional and unintentional (pair) Case 73, Case ;74

Contact, expected and unexpected movement (pair)  Case 77, Case 91

Mark-room, Direct corridor/tactical rounding:  Case 75, Room given room taken  Case 63

Hindering another boat by breaking a rule Case 34, not breaking a rule Case 78

Keeping a lookout:  Case 107

Redress:  Errors in recall signals:  Case 31, Case 79

Race/Protest Committee never required to protest;  primary responsibility with racers:  Case 39

Hook finishes:  Case 45, Case 82, Case 129

Sailing the Course, NSC: Case 90, Case 106, Case 112, Case 128.

Deception, False hails:  Case 47

Hearing Protests together:  Case 49

Facts and Conclusions  Case 104

Good post John thanks

Thanks, John!  I have my homework cut out for me.
-V

There's this *amazing* website that has little pop-up case references next to each rule, with a helpful summary of the points therein. It references the Judging manual too sometimes. There's a small fee but well worth it for the functionality, as well as being able to deliver regattas on it.  It's called racingrulesofsailing.org ;-) 

Seriously - I use that as reference for all the WS cases. Of course, back to the original publications for definitive text but as a quick-reference it's invaluable. It directs you to the relevant case rather than reading all the cases and trying to backsolve for a given incident.