I do this for my sons school. I basically wanted to be on the sidelines to get better shots. So a couple of years ago I asked one of the coaches if I could get closer, he asked what I was doing with the photos and I told him just putting them on fb for the kids. Long story short, after speaking with the principal and ad, I take photos at anything I want. It gives me access to learn and the school gets free sports photos for their yearbook, internet, whatever they want in sports. Its a small community, and the school does not have the funds to really pay anyone. So I scratch their back and they scratch mine. I signed a form saying I am totally responsible if I get wiped out in a football game lol and away I went. Like others have posted, just stay out of the way. Every time I have to pass by a coach I say excuse me, etc. It also helps if you get plenty of shots of the coaches in action as well. Their wives like seeing them too. Also make a deal with the coaches, as they age and get fatter you will stay above the waste. They love that lol. Just be nice. Most school principles love any thing you can do for the school. I have learned a ton, plus it helps to befriend any "old" photographer as well. A man named Frank is 80 on my sons sidelines, but he has been taking photos since the 50's. Super nice guy. Here is a link to my flickr account and what Ive done this year: https://www.flickr.com/photos/51526542@N02/sets/
I still have a lot to learn but from where I came from 2 years ago, I never would have learned so much if I wasnt doing the high school stuff. Im still culling a lot of my photos from this past season so dont get too bored, and the kids love the hdr stuff, for their website and their yearbooks............just be nice. Everything was with a t2i and a 70/200L non is. Thats all I have for equipment and a 2x tc.