As the popular bumper sticker says, "Skateboarding is Not a Crime," and many cities have skate parks where skateboarders can get together to practice tricks or just mess around on their boards. It's outside of designated areas where you sometimes skate the line between legal and illegal.
Different states have different laws about skateboarding in public places. Some towns allow you to skate on the sidewalk, as long as you're not doing tricks or anything else that could be considered reckless. Other cities ban skateboarding in public areas altogether.
In New York City, for example, skating "recklessly" on the sidewalk is illegal [source: Willis]. But riding on the sidewalk (or most public roads) at a low speed is OK. Meanwhile, cities like San Francisco make it illegal to skate on the sidewalk at all, and skaters can get a traffic violation for doing so [source: SF Appeal]. It's also illegal in San Francisco to skateboard in the street!
Skateboarding laws are usually health- or traffic-related and sometimes distinguish between using your board as transportation or for recreation [source: FindLaw]. The idea is that if you're using your skateboard to commute to work, you're behaving very differently than if you're trying to perfect your grind on a stairway railing.
There are also liability concerns about skateboarding on private property. If you fall while doing an ollie in a shopping center, you can sue the shopping center [source: FindLaw]. Not only can skateboarding on private property be a liability concern, but the law considers it a public safety issue, and some towns have gotten stricter about enforcement. In Fallbrook, Calif. in 2008, police began cracking down on skateboarders in shopping centers, saying that shoppers couldn't walk safely on the sidewalks because of skateboarders [source: Ramsey].