Have you ever been baffled as to why you lost an adjudicated competition? Scoring is always subjective. Even math teachers expect you to "show your work."
Who's taste is best? Are we born with an innate sense of fairness, or must we strive toward it?
Inadequate judge instructions cause baffled entrants. An adjudicator's job should not be to give their opinion but to determine if and how well the submission met the requirement. With this aim, a rubric provides an excellent guide.
What
Rubrics are scoring criteria, usually presented as a table with aspects being scored as rows and levels of achievement as columns. Some use a rubric only to help calculate the final score, but this is not its full purpose.
Scoring rubrics were invented to 1) Give students or entrants a clear understanding of how their work will be scored, and 2) Help graders score consistently.
Rubrics should be provided to entrants before submission. After scoring, it should be sent back completed.
Why
We want to know which student has the highest grasp of the material or ability to perform. A perfect method to know is beyond human reach, but can we strive for greater fairness?
A rubric is a step toward greater fairness.
