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And also, if you can see what the press passes look like just make yourself something along those lines, act like you're supposed to be there, and don't get in anyone's way. For smaller games/teams whatever, the event staff most likely won't take a second look, or even care.
Did I read this right? Find out what the "press passes" look like and make something to look like it to "act like you're suppose to be there"? Hot damn!! This is easily in the Top Five of all-time WORST advice I've ever read on this forum. Take this advice and you risk becoming a 16-year-old who is black listed and will find it tough to get credentials to anything. If not forever, certainly for a very long time. Please don't do this. Gawd.
You've been given some good advice about MiLB from some guys who know what they're talking about. And, like others have said, you can make great images from shooting sports at your high school or other schools in the area. Access is great and your portfolio won't be lacking one bit if you can make great images from shooting high school sports. Take advantage of the many sports photography opportunities right there with your own school.
As a former newspaper reporter, I've always taken the approach that it never hurts to ask. So, just ask. I'm guessing the race track might be a bit of a stretch because tracks often seem to have an age restriction. But again, it doesn't hurt to ask.
My son started shooting high school and D2 sports when he was 11 years old, and has had opportunities to shoot D1 sports on a regular basis, NFL, NBA, NHRA, concerts, rodeos, and a lot of other events. He's done it by being respectful and polite to other photographers and not cheering or show bias toward a particular team. He also pays attention to how other photographers conduct themselves and is quiet and works in the media room. In short, let your images stand out; don't stand out as an obnoxious person who no one likes to be around.
Good luck and keep us posted how things go.