What Are Drops in Rocket League?
You can earn Drops as Challenge Rewards and on the free track of Rocket Pass.
A Drop adds an Item to your inventory when opened. These Items come in every rarity type from Sport to Black Market.
The rewards from Drops cannot be exchanged or swapped for other items by Player Support, however, they can be exchanged using the trade-in function. For more information, consult the article What is the Trade In function in Rocket League?