A relatively new addition to Clash Royale are Clan Chests. You earn a higher Clan Chest reward the same way you get chests in game or work towards the daily Crown Chest, by beating others in multiplayer. Only every single players victory gets added to the Clan Chest. Which helps the reward get bigger. These are once a week, and last from Monday-Friday.
As long as the entire clan participates, you'll get a bigger reward from the Clan Chest which helps us in the game. As a reminder, if you leave your clan for any reason during an active Clan Chest, you don't earn anything. It gets taken away. So don't go clan-hopping while one is going, or you'll miss out after all that hard work.
Each Clan Chest where we got past level 4 in my clan, I've earned a Legendary card. So it pays to take part in this weekly event.