https://www.pcgamer.com/rocket-league-loot-box-odds-revealed/

After a year overflowing with loot box and pay-to-win controversies, loot boxes are now steadily being phased out, with many studios adopting battle pass-style business models, outright removing loot boxes from their games, or disclosing the odds of their loot boxes to maintain transparency. Rocket League developer Psyonix joined the latter group earlier today: the math behind Rocket League's loot crates is now out in the wild thanks to a recent blog post. Here's how they break down:  

Psyonix also explained how Rocket League's crate system determines rewards. Simply put, when you open a crate, the game rolls for item rarity, then for an item within that rarity (items of the same rarity are equally weighted), and finally for Painted or Certified attributes.