wow, marching band post....bit surprised to see this. spent 12 years in it myself (last fall being my final season)
anyways, dont hate me, but i wouldnt call it a sport myself....tho, its just as hard as any sport out there. the challenges, physical demands, discipline are just as tough. I still remember marching on an old field in the rain, hitting some random holes/puddles that were getting mud up to my knees, and just having to keep moving, keeping the horn facing the right way, and not let it distract me.
honestly, i challenge just about anyone to try to hold some of these horns/instruments up for 10 minutes straight(where im from, proper position was horns points to the press box, meaning above parallel) just try to stand there and hold it for 10 minutes...or even 5.....let alone a full rehearsal. this with out the heat, moving, playing, etc. I played a baritone, and due to where your hands sit on it, and how big it was to start with, its easily one of the hardest to carry (not to take away from any other instrument, everyone of them gets heavy fast..)
This all ignoring having to remember your music for how ever many songs your putting on the field, remember your position, the positions of those around you, any visuals that may be in your show(couple years ago we had to do some michael jackson dance on field in the middle of a song....)
anyways, i think this has all been pretty well covered, no point in me saying it all again.
tho i am curious, how many have had to do 4 to 5 marching (4 steps to 5 yards, as opposed to an average marching pace of 8 steps to 5 yards, explaining for those who aren't in band and dont know, and i'm unsure how its taught in other places :p )