Sentence:  The <WSD>headspring</WSD> is a unique vault because it calls for a bent arm support and the touching of the horse with one's head. 
Meaning of the word marked with <WSD> tags:  A move in which the gymnast places both hands on the mat with the top of the head about 6 inches in front, pushes off with the hands while flipping the legs overhead, and lands on the feet.