Girls (mostly) who spin a flag, rifle, and/or sabre( or sword). They are a mix between cheerleaders, dancers, and football players. They work their asses off to look good out on the field. Color guards are always together in shows, and strive to look the same. They are the best part of marching band.
Bob: Hey, whose that hot chick wearing a unitard and spinning a flag?
Steve: Oh, that's Sally, she's on color guard!