So, towards the end of the Njal saga there's a courtroom drama where the accusing side attempts to discredit the defending side on the basis that they have bribed their lawyer. So Mord, who is leading the accusing side, demands that 6 judges are removed from the those presiding over the case, and the rest of the judges pronounce the verdict.
Apparently, that was a huge mistake, and he should have removed 12 judges instead, so the total of the remaining judges if three dozen. That was apparently not very widely known (it seems there are very few people among lawyers and other judges that are aware of this), yet a grave enough mistake that threatened to make all of the accusing side (the good guys) exiles and outlaws, effective immediately. Questions:
What were the reasons behind removing judges from the case? How did this practice work?
And why was it so grave a mistake that people could have literally gotten themselves killed over this?
Not really a court room since it's at the Althing, but the point here was a form of jury selection; both sides would remove six judges each, but if the defendant refused, the plaintiff would remove another six himself. Flosi and Eyjólfr correctly count on Mörðr (chapter 140) being too impatient for a verdict that he'd forget to remove another six if they declined. Hence, as we'd say these days, the case was dismissed on a technicality, because according tot he story only three twelves can issue a verdict.
There's no real reason to think this was a general custom; in fact there's reason to think otherwise because the story itself explains the creation of this 'fifth court' (fimmtardómi) and its rules, and then repeats them again in the Flosi-Eyjólfr dialogue. It's likely just an invention of the storyteller to create the technicality and thereby precipitate the events that follow.
Mörðr & co aren't threatened with being outlawed (which is just short of a death penalty) for this mistake, the case is dismissed. What happens is that Eyjólfr then moves to immediately begin his counter-suit demanding they be outlawed.
I don't think this reflects so much on the legal system so much as it creates a reason for Þórhallr to go crazy and start violence at the þing, leading to the violent culmination of the story and its resolution.