R. A. Denardi, F. Romero, T. A. C. Oliveira, S. L. Silva, B. Travassos, and U. C. Corrêa, “The influence of defender’s positional gap on the aces in the sport of volleyball”, J. Hum. Sport Exerc., vol. 12, no. 2, pp. 286–293, Jul. 2017.