When Judges are assigned to Competitors (more on auto assignments here), they will be preferentially assigned to Competitors in their matching Tag. 

This may be affected by your selections on the Event Dashboard page, like:

IMPORTANT: If Judges are in multiple Tags, they may be assigned Competitors from ANY of those Tags. There is no order preference of the Tags.  
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If you want to restrict judge matching so that judges do not get assigned any projects outside of their Tag, Wildcards must be set to -1 (negative one).

Note: Tags used to be called Groups.