Muslimin, Muslimin, et al. “Free Passing Training Model for Improving the Underpassing Skills of Male Volleyball Players Aged 12-14 Years”. Altius: Jurnal Ilmu Olahraga Dan Kesehatan, vol. 13, no. 1, May 2024, pp. 80-92, doi:10.36706/altius.v13i1.63.