That said, my personal belief on balance goes something like this
How much is Heart in every roll, or Toughness, or Conditioning?
Every player has a "balance" attribute during the play, much like morale and energy.
Lots of things that happen in plays take balance away, just like you lose energy and morale.
The balance skill helps you lessen your balance losses and also increases your balance recovery. So I rather doubt balance is directly in your catch pass roll, for example, but catching a pass can give you a big balance loss, so if you want to stay standing and be able to start running, balance matters a lot. Similarly to blocking interactions - it's probably not directly in the block/break block rolls (but it could be?) but the result of the rolls leads to loss of balance for one or the other.
Your current balance state is also probably a spectrum, not just "standing" and "fallen over" - and like morale and energy, being at less than 100% balance could possibly affect every skill you have. So in that respect, balance is in "every roll".
Again, that's all my speculation. I don't have anything like quotes from dev or whatever to back it up and it's quite possible it doesn't work that way at all, but it would make sense based on what we know.