There actually is kind of a history with betting and CS; the meme "bet t all" and a picture of a swat policeman petting a cat references this.

Basically pre-round or mid round you could bet some of your in game currency on a side winning. This let you recoup lost money which you could use to buy guns etc. the next round.

I always thought it was just a fun addition to the game but if you did it real time, round by round, with real money it could be cool too.