It was going to be troops marching in formation, but this is so much nicer.
Do you remember field days when you were a kid? Going outside, competing in games, maybe winning prizes. Sort of an end of the year tradition. (At least in my schools.)
Well, would you believe that term, Field Day has a military meaning?
Starting in the 18th century the military used the word to refer to a day that was set aside for maneuvers and reviews, as a way for the troops to show off on the parade ground. Just like in school.
Of course, there is a negative connotation to the term as shorthand for someone making a big deal out of something. You know, “don’t make a field day out it.”