The importance of this research lies in highlighting one of the modern training methods that may contribute to improving the athletic performance of handball players, whether on the physical or tactical level. From the perspective of physiological variables, repeated-sprint training at maximal and sub-maximal intensities is employed to enhance anaerobic capacity and increase the efficiency of the nervous system. The research problem emerged from the observation that many coaches focus heavily on offensive skills, neglecting the fact that an offensive mistake results in losing the ball, whereas a defensive error grants the opponent a scoring opportunity. Additionally, poor performance results may be attributed to the inability of the body’s functional systems to withstand the demands of continuous and variable motor performance, as well as the noticeable delay in physical preparatory aspects such as speed of movement across the court, reaction time, and decision-making during defensive situations like intercepting or clearing the ball. Despite the importance of these aspects, training programs for players under 15 years of age still require further development in defensive performance and movement speed, which in turn influence physical abilities such as lower-limb explosive power and anaerobic functional variables.The study aims to: Design repeated-sprint training using maximal and sub-maximal intensities for handball players under 15 years of age, and identify the effects of this training on the alactic (phosphagen) anaerobic functional variable, lower-limb explosive power, and individual defensive movement among players in this age group. The researchers used the experimental method with a design of two equivalent groups (experimental and control). The research population consisted of players from the Specialized Handball School in Baghdad under the age of 15. The sample was intentionally selected and consisted of (20) players, randomly divided into two groups: (10) players in the experimental group and (10) in the control group. Results showed that repeated-sprint training had a significant positive effect on the development of lower-limb explosive power (right and left) and on improving the phosphagen anaerobic functional variable in the experimental group. The designed training also led to significant improvement in individual defensive movements, including ball interception and clearance. A lesser degree of improvement was observed in the control group compared to the experimental group.