It all depends on the glasses you get. I haven't had a sport that required me to need contacts. Course my glasses are pretty much glued to my face. I can shake my head side to side, up and down, they won't fall off. Only time they've fallen off is when I face planted while snowboarding. Course a contact would pop out too. Since then, I've worn goggles while snowboard. Keeps my glasses on, but wouldn't keep a contact from popping out.
If you look at the side of my head, there's actually an indent from my glasses.
Yeah, my glasses never come off either when I run around or play sports. Of course, they fly off if I get hit in the face during dodgeball, but that's different.
I have an indent too, but it's more like a barely noticeable line on my nose from the bridge. Can barely see it, but it bothers me. I hope it goes away if I ever stop wearing glasses.