Tim May thinks he knows why fans love motocross freestyle and BMX stunt bikes. ‘‘People love to come and watch a train wreck,’’ the organizer of the Yankee Lake Extreme Sports Music Festival said. ‘‘It sounds bad to say, but why does everyone watch NASCAR?’’ The perils of the sport helped inspire the idea for the event planned Saturday out at Yankee Lake. May’s nephew, Garry Robertson, used to be a motocross racer before switching to motocross freestyle shows. Last year he broke his back in a motorcycle accident. ‘‘While he was down, I started bending his ear,’’ May said. ‘‘We put this together between the two of us.’’ Robertson is back on his bike, and he and other nationally known riders like Jack Rowe and Clint Esposito will be showing their moves. Robertson said some of the riders performing Saturday qualified for the X-Games and the Dew Tour but were unable to participate due to injuries.