A. Olmedilla Zafra, E. Ortega, M. Ato, F. J. Lozano, E. Garcés de los Fayos, and F. J. Ortín, “Infringements of the laws of the game and youth soccer categories: A descriptive study”, J. Hum. Sport Exerc., vol. 5, no. 1, pp. 71–83, Jan. 2010.