Premier Ball

A Premier Ball is a special device for capturing a Raid Boss.

Details
Based on which Trainers controlled the Gym, how much each Trainer contributed as a team during the Raid Battle, each Trainer will receive a variable number of Premier Balls. These can be used to capture the Raid Boss, once it has been defeated.

Trivia

 * The Raid Boss will be very difficult to capture, because it tends to move a lot more frequently than Pokémon in the wild.
 * Unused Premier Balls are discarded after a Raid Boss encounter.