Complex sentence: A related, traditional sport, paddleboarding has been done kneeling on a board and paddling with the hands, similar to a butterfly swimming stroke, but using a paddle is now sometimes also called paddleboarding.
Split into simpler sentences: A related, traditional sport, paddleboarding has been done kneeling on a board and paddling with the hands, similar to a butterfly swimming stroke. However using a paddle is now sometimes also called paddleboarding.