When I'm watching some games at my LGS's FNM or casual tournaments, I'm never sure if I should or shouldn't interrupt a game to say “don't forget this” or “you can”t do that", etc. Do you have a link that I could read other than JAR (Which I've read 5 times I think), or can someone give me the major cases and an example for each of these where I should be interrupting?

Thanks in advance!

You should avoid preemtively stepping in, as you never know - they might remember in time :)

If you see any of the Common Errors as described in the JAR occur, you should step in. The JAR doesn't distinguish between “The Judge saw it occur” and “The players called a Judge”. Either way you help them out and fix and educate as appropriate. The only exception might be some missed triggers - depending on how competitive the crowd is, you may wish to leave them alone if you see a missed trigger occur. However that's mostly up to you and your community.

Hey Samuel.

We are going to be starting posting more regularly on the Judging at Regular REL blog (there is not much there right now, just some updates information), and are currently looking for topics which people would like more information on. I will add ‘When to intervene at Regular REL’ to the list, and will start a new topic on this forum linking to the posts when we start making them.

Mark has summed up the general rule, though - you should only intervene in a match if something illegal actually happens, or if a player calls you to asks you a question. Even at Regular REL, we don't play the game for the players!

If anyone else has topics that they think could be useful to cover in a bit more detail, please feel free to let me know!

That's a very good idea. But can you define what's illegal? You can clearly not redirect counter spells to Spellskite, but what about a player that forgets his Dark Confidant trigger? What if he forgets to gain life with a life link creature?

What's the difference between illegal action and illegal board state? Should I be intervening in both?

An action which is illegal is one which is in violation of the Comprehensive Rules - it is one that you just cannot do. As Mark pointed out, fix guidelines for Common Errors are presented in the JAR. Of the examples that you give, the Spellskite and the Lifelink errors are both ones which you should intervene on if you see them occur (not before they occur, just because you think they might, mind) - they are illegal and they need to be fixed as soon as possible.

The Dark Confidant example is a Missed Trigger, and as such can be treated a little differently. We encourage judges to gauge the mood of their group in order to decide whether a judge should intervene on this one kind of error or not - if players are more competitive (for example, you are at an FNM where the local crowd uses it to test for PTQs), it is better not to intervene as players accidentally forgetting their own triggers is a thing which we allow them to do. If the players are more casual or less experienced (such as at a Prerelease), the focus becomes much more heavily on education, and so stepping in and pointing out missed triggers before allowing players to resolve them may be more appropriate.

TL;DR - if something happens which violates the CR, it is illegal. If this is anything except a trigger being missed, you should intervene. If it is a trigger being missed, it depends ;)

On illegal action vs. illegal game state: the best illustration I can give would be to say that an illegal action would be casting a green Aura targeting a creature with protection from green. An illegal game state would be that creature being on the battlefield with that Aura attached to it. Yes, you should intervene in both!

Originally posted by Samuel Tremblay:

That's a very good idea. But can you define what's illegal? You can clearly not redirect counter spells to Spellskite, but what about a player that forgets his Dark Confidant trigger? What if he forgets to gain life with a life link creature?

What's the difference between illegal action and illegal board state? Should I be intervening in both?

Missed triggers are not illegal per se. If you think the player missed a generally detrimental trigger (like losing 1 life to Torment's Herald) or intentionally missed a trigger, you would step in. For the most part, you should not step in to point out missed triggers unless you're comfortable that they're detrimental and should encourage other players to do the same. Even better, ask them to ask you first.

Not gaining life with a lifelink creature is not a trigger. That's a game rule, and they have to do it. If they forget, step in when they try to take another action that clearly shows they forgot it and remind them that they have to gain the life. Hopefully you caught it before a backup is really difficult. If so, do nothing!

Illegal actions are something that may or may not result in an illegal board state. A player Spellskites a Counterspell. The counterspell goes to the graveyard. You walk up. This is not an illegal board state- spellskite is a permanent, counterspell is an instant in the graveyard. You can put 2 and 2 together and figure out that something illegal happened and ask about it.

An illegal gamestate is an ongoing violation of the game rules. Think Unflinching Courage on a Stormbreath Dragon. It was an illegal action to target the dragon with the courage due to protection from white. Protection from white should also remove any white enchantments from the dragon during state-based actions, so this is a currently illegal gamestate. If you can't back up to when the UC was cast, perform necessary state-based actions to clean up the game and continue, reminding them to be more careful.

For a real brainteaser, you see a Stormbreath Dragon exiled with Detention Sphere. You know that an illegal action happened to target the stormbreath dragon, but what if it's too late to backup? Even though they're “linked”, there's nothing wrong about a dragon in exile, and the d-sphere is perfectly legal in play. Here, an illegal action has resulted in a weird but legal game state.

The take-home is that you should ask questions concerning illegal actions or illegal game states. You can fix illegal actions by backing up if it's not too complicated and disruptive to the game. If you can't, the next step is to fix illegal board states- you have to do this. After that, educate them why what they did was illegal.

Originally posted by Evan Cherry:

For a real brainteaser, you see a Stormbreath Dragon exiled with Detention Sphere. You know that an illegal action happened to target the stormbreath dragon, but what if it's too late to backup? Even though they're “linked”, there's nothing wrong about a dragon in exile, and the d-sphere is perfectly legal in play. Here, an illegal action has resulted in a weird but legal game state.

Once you've passed the “if” part of interrupting, it's useful to consider the “how” as well. If you see something you think is wrong, it may be that you are missing something about what happened in the past.

Rather than say “Hey, your Stormbreath couldn't be targeted, so something bad happened. We're going to leave it, etc…” it would be better to approach with a question. Maybe “Is that a Stormbreath under the D-Sphere?”, and maybe a followup of “How did it get there?”.

If they say something like “I cast that a couple turns ago”, you can explain the problem and the “fix”, that way they don't make the same mistake going forward.

If they say something like “he Turn'd it, then D-Sphered it”, you can say “Ah”, and move on. (It's legal to do and not entirely out of the question, maybe there was some damage prevention so that Burn wouldn't kill it off and they really wanted it gone?)