If I receive a large sum of money (going towards helping fund athletics) from a person who is not family, does this count as personal income? I know there have been cases where people have been audited with monetary amounts gained on platforms such as gofundme.
The CRA has a very clear statement:
Amounts received as gifts are not subject to tax in the hands of the recipient.
The issue, however, is in defining "gift."
Sometimes money is given to you but doesn't really belong to you. This is common within a family: mom and dad would pay a high marginal tax rate on the interest on their nest egg, but while you're a student with no income, you won't pay any. It's not really your nest egg in the meantime.
Other times a gift is really your income. Like a corporation just happens to give you the exact same cash gift every two weeks, and you do some volunteer work for them as it happens. Purely a coincidence, no? No.
and other times your gift or donation is really you selling something to a person. That doesn't make all of it income, but may create some real income.
What you're describing sounds like a scholarship and is therefore probably not income. But it matters whether the "not family" is the team you play for (you need a ruling on whether it's income or not) or a corporation sponsoring you for endorsing their shoes, or whatnot.
If it's enough money that the tax on it matters, get an opinion from the CRA. If it's a few thousand from a neighbour who hopes you'll win gold, you didn't ask for it, it's not an ongoing (monthly or yearly) thing, and it's not contingent on you doing certain things, then you can feel pretty confident you fit the definition of gift.