I abide by the rules and always refer to them as "duals." In fact, I do believe I remember correcting someone on this matter in seasons past.
While one might consider two teams competing against each other a "duel," whenever I think of that word it conjures up images of moustachioed men slapping each other with white gloves and declaring they have been wronged. Thus, dual is the term for me.
However, if captains were to come out before a dual and slap each other were white gloves and declare that their team's honor had been besmirched by their foe, I would gladly change my opinion on the matter. KSHSAA--make this happen.