Indah Zunita, et al. “The Relationship Between Self-Confidence and Concentration With the Ability to Smash Volleyball Athletes 12-17 Years Old in Pervas Club ”. Jorpres (Jurnal Olahraga Prestasi), vol. 21, no. 2, Sept. 2025, pp. 57-66, doi:10.21831/jorpres.v21i2.95718.