Three Card Monty
Whenever a police car passes by, you can observe how quickly these games disperse. Sidewalk card games are both illegal and fraudulent for some very good reasons.
Scenario Two or more people are standing around a cardboard box on a busy street trying to win money by choosing the correct card out of the three cards shuffled. You notice that someone seems to be winning; this person is usually working with the dealer to lure people in. People who work these scams know that it will be less suspicious to plant a women or someone in a business suit in the game. The shuffler will purposely lose the first few rounds to get you to bet more money. At this point, if you take your wallet out, someone may grab it and run -OR- it will be pick pocketed as you watch the game. If by some fluke you win, you may be followed and mugged.
How to avoid this
The hand is quicker than the eye and these are pros. Don't play - YOU CANNOT WIN!