if i play rockband while tap-dancing, does that make rocktapping a sport? no, it does not.
marching band is not a sport because it does not meet the criteria to be a sport, it does not have set rules, it does not have a competitive edge, it does not require physical skill or prowess outside of "walk in formation while holding instrument." you forced cheerleaders and football players to march with your stuffty instruments, they probably agreed with you so you wouldn't throw a hissy fit. just because you feel what you're doing should be a sport does not make it a sport. lifting weights is not a sport, running on a treadmill is not a sport, scuba diving is not a sport. these things are not sports, and neither is marching band.