Is gambling a crime in California? You'd think the answer to that question would be simple, but it's actually pretty complicated.
Let's start with card, dice and domino games like poker and pai gow. Under Penal Code 330 PC, California's gaming law, it is generally legal to play these games for money--as long as there is no "bank" or "house" that participates in the game or takes a percentage cut of all bets or winnings. So a friendly game of poker among friends is usually no problem.
But if there is a bank or a house participating in the game or taking a cut, then the game becomes an illegal "banking" or "percentage" game under PC 330. In that case, anyone who participates in it may be guilty of a crime.
What about betting on sports events? You can be convicted under California's bookmaking law (Penal Code 337a PC) for running or assisting with bookmaking or pool-selling operations that help people place bets on sporting events. And you can also be prosecuted under that law for placing bets through these kinds of operations.
BUT you are not guilty of anything more than an infraction if you participate in a betting pool where no one acts as "bookie" or makes a profit off of the pool by taking a cut of bets, as long as the total amount of bets is no more than $2500.