Indah Zunita et al. 2025. 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). 21, 2 (Sep. 2025), 57–66. DOI:https://doi.org/10.21831/jorpres.v21i2.95718.