I had a strange issue come up earlier this year at my first GP after passing my L1 test.

I was spectating (as a fellow player) a match that my friend was playing in. This was one of the last matches of a Super Sunday Series round and a floor judge had come over to watch turns 0-5. On turn 1, Ajani played a wild instincts to fight a creature with deathtouch. Nissa put the deathtouch creature in the graveyard and Ajani proceeded to attacks.

With a judge watching over the match, I didn't want to interfere at first, but when neither player nor the judge saw that Ajani's creature should have been put in the graveyard as well, I called the judge away from the match and explained what was missed. He proceeded to confirm the events with the players and backed up to before attacks and put Ajani's creature in the graveyard, issuing both a FMG warning.

My question is what responsibility do we have as a spectator when a judge is already present at a match?

Your responsibility as a spectator is no different when a judge is present
than at any other time - you are not required to call attention to errors,
but if you do, you must ask the players to pause while you inform a judge,
not try to fix the problem yourself.

Likewise, your responsibility as a player is no different when a judge is
present than at any other time - if you notice an error in your match, you
must call attention to it.

The judge is not a “table judge”, there to catch every possible game error.
He is there to administer the end of round procedure and get the match
result. If he catches a play error, great, but it's not his first priority
to watch for them.

I know this is the Comp REL forum, but I do want to add something I was made aware of recently to this discussion which I believe to be worth noting.

At Professional Level (which does fall outside of this situation), responsibility of a spectator is slightly different. Spectators are not to pause matches. They are still asked to get a Judge's attention as soon as they can. The Judge can then pause the match and being an investigation.

I believe Professional Level is used at Day 2 of GPs and on Pro/World Tours.

I'm interested in the fact that both players got FtMGS for this. Neither got the GRV?

Based on the situation described, Ajani should have gotten a GRV (and Nissa
still a FtMGS).

Originally posted by Dan Collins:

The judge is not a “table judge”, there to catch every possible game error.
He is there to administer the end of round procedure and get the match
result. If he catches a play error, great, but it's not his first priority
to watch for them.

I just want to add on to this that it isn't a failure of a judge to not catch an error in a match he is nearby. There's a large number of things that a judge could be paying attention to other than the exact play at hand.

If you're curious, here's some of the things I'll do when I stop by a table that besides paying attention directly to the match at hand:

Check life totals (to see if they're the same on lifepads)
See if there's a time extension
Try to catch myself up on the game state
Look at libraries to see if there's anything obviously fishy going on (without picking them up)
See if any of the cards look like obvious sideboard cards in game 1.
Try to figure out what deck they are playing.
Seeing if they have any handwritten tokens or are using imperfect tokens (so I can get them a better one at limited events)
Watching a specific player for slow play
Try to figure out why a specific card would be in a given deck
Watching a specific player for fishy behavior