sentence: Two dirt bike riders dressed in full motocross gear sit on their motorcycles. sentence:   A motocross rider rides his red dirt bike over some small Whoop-De-Dos. sentence:  The camera man pans across the motocross course with different riders riding on different parts of the course. sentence:  A group of motocross riders perform some jumps at high speed from multiple directions. sentence:  A group of motocross riders ride on the motocross course performing tricks and other riding skills.