Tom Clancy's Rainbow Six Siege is a popular tactical shooter from Ubisoft about confrontation between Terrorists and Counter-Terrorists. The game had a lot of problems at the release, but the developers fixed most of them and made R6 Siege quite comfortable and fun to play. Right now it is a descent competitor to CS:GO.
Ubisoft systematically improves Rainbow 6 Siege esports scene, including major tournaments and competitive leagues in many regions. This fact motivates a lot of esports organizations to sign up rosters with professional players.