A more thorough explanation:

The Court of the Lord High Constable and Earl Marshal was a court that had authority over various military matters, including cases of treason, prisoners of war, and disputes over coats of arms. The Lord High Constable and the Earl Marshal were the top military officials during the reign of the Norman kings.

For example, if someone was accused of treason, they would be brought before the Court of the Lord High Constable and Earl Marshal to be tried. If there was a dispute over a coat of arms, the court would have the power to settle the matter.

After the office of Lord High Constable was forfeited in 1521, the court continued on as the Court of the Earl Marshal, but its jurisdiction was reduced to questions of chivalry only. This means that the court only dealt with matters related to knights and their behavior.

One example of a case that the Court of the Earl Marshal might have heard after 1521 would be a dispute over whether a knight had acted honorably or not. The court would have the power to decide whether the knight had followed the rules of chivalry or not.