Propel moshing is a skill that only long-haired heavy metal fans can develop properly. To propel mosh is to do a circular motion with your head so that your hair moves like a propeller. It might be a good idea to crouch a bit at the same time and hold your knees / thighs for support so you don't fall over. It is a sight to behold, especially in good heavy concerts where the whole first line of concertgoers are doing it. Or the band. Only a true pro can do it while moving around and jumping at people.