You will only lose a good friend if you continue liking her after you've rejected her. Then it's awkward for you, and if it's awkward for you then it's awkward for her. And you won't end up talking. So if she says no (which is unlikely IMO) then stop liking her. Sorry.
Of course this awkwardness can be overcome if you're confident in yourself (in maintaining a standard friendship) but I'm getting a lot of self-doubting vibes from you.
From past experience: don't tell anyone that you like a person. They will find out sooner rather than later and if they don't like you it's super awkward
But anyway. Wait until after trails and then ask her out. Screw this sports game or whatever, the point of dating is to know the other person better. You can do it better over coffee/ drink/ even walking and sitting at a park bench.
With everyone there is always a risk of her saying no. There is NEVER a right opportunity. Like I've said before, if you don't ask her out you're probably not mature enough for a proper relationship. You also need to be confident in yourself within a relationship, clingyness is a turnoff for (most) girls.
You're not signing your life away. It's just dating. BF/GF stuff comes later. (and that may even be harder than asking her out on the initial date lol).