[Procolsaurus]

Each robot on the field has the option of starting with their own ball in autonomous. One of these teams could then choose to start with their ball outside their robot, for an alliance partner to pick up or somehow deposit their ball from inside their robot into an alliance partner. The alliance partner could now shoot their own ball and the second ball.

Note there are no rules against possesing multiple balls in autonomous (or even during teleop?).

I believe this to be accurate but have not re-read the rules about this in a while.