Olmedilla Zafra, A., 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”. Journal of Human Sport and Exercise, vol. 5, no. 1, Jan. 2010, pp. 71-83, doi:10.4100/jhse.2010.51.08.