Every 3 days. You compete on a board with up to 1,000 players, split into five tiers by position. When the period ends, the players who scored get chests for their tier:
- Top 20%: 2 Legendary Chests
- Next 20%: a Legendary Chest and a Rare Chest
- Next 20%: a Rare Chest and a Common Chest
- Next 20%: a Rare Chest
- Last 20%: a Common Chest
Open the Leaderboard and tap Claim rewards to collect them.