Sports in the X-treme

The X Games, ESPN's yearly sporting event for daredevils and adrenaline junkies, begins this week in San Francisco. From Friday through July 3, more than 450 people will compete in aggressive in-line skating, bicycle stunts, sky surfing, street luge, motocross, wakeboarding, sport climbing, snowboard big air and, of course, skateboarding--the original "extreme" sport that gave birth to this yearly event, and its name. Following is our primer for armchair athletes on skateboarding's basics.