GSGO (Counter-Strike: Global Offensive) is a very popular game, you can buy keys on Steam to unlock crates in-game that give you prizes.
These prizes can be instantly sold for money or added to gambling sites to create pots that are won by individuals.
The good guys over at h3h3Productions have released this video which basically shows that various YouTubers have been encouraging their followers (many under 18 years old) to gamble on what turns out to be a gambling site owned by those very same YouTubers.