The activity that is not a gymnastic activity is "Hockey". The other options, backward roll, crab walk, and hand spring, are all common gymnastic activities. Backward roll is a basic gymnastics movement where an individual rolls backward in a tucked or extended position. Crab walk is a crawling movement that requires an individual to move on all fours with their stomach facing upwards. Hand spring is an advanced gymnastics skill that involves a frontward flip onto the hands and then pushing off them to return to a standing position. On the other hand, hockey is a team sport played on a field or an ice rink, where two teams use sticks to hit a ball or a puck towards their opponent's goal.