Simple Summary Locomotor performance is constrained by how players generate and transmit force into the environment. Thus, understanding the factors that influence locomotor performance is important to optimizing players' performance. The assessment can be performed while applying an intermittent progressive multistage running test. However, the performance of such tests depends on different physical qualities. Although many studies present relationships between performance in multistage tests and other physical qualities, there is a lack of evidence regarding the relationship of anaerobic speed reserve (difference between maximal sprint speed and velocity at maximal aerobic speed) with other physical variables. This may be relevant for identifying the factors that can optimize locomotor performance. Our study was conducted to identify the relationships of performance at a multistage test (30-15 Intermittent Fitness Test) and anaerobic speed reserve with the sprinting, change-of-direction, and neuromuscular capacities of youth soccer players. The findings of this research revealed that performance on an intermittent progressive multistage test is correlated with neuromuscular, sprinting, and change-of-direction abilities, while anaerobic speed reserve seems to be relatively independent of those qualities. This study aimed to determine the relationships of locomotor profile (combination of a player's maximal oxygen uptake and running economy)-measured by the final velocity attained at 30-15 Intermittent Fitness Test (V-IFT) and the anaerobic speed reserve (ASR)-with the body composition, countermovement jump (CMJ), sprinting performances, and change-of-direction (COD) ability of youth soccer players. A cross-sectional study design was implemented. A total of 124 youth soccer players from different age groups (15, 16, 17, 18, and 19 years old) were voluntarily recruited. ASR was determined based on the difference between maximal sprint speed (MSS) and V-IFT. Players were tested for the following measures: (i) body composition (body mass and body fat percentage); (ii) CMJ (height of jump); (iii) sprinting time measured at 5, 10, 15, 20, 25, and 30 m; (iv) MSS measured in the best split time (5 m) over the 30 m test; (v) COD ability (time, asymmetry index); and (vi) final velocity at 30-15 IFT (V-IFT). A Pearson product-moment correlation test was used to examine the relationships. Height and body mass exhibited large correlations with V-IFT (r = 0.835 and r = 0.699, respectively) and small correlations with ASR (r = 0.177 and r = 0.256, respectively). The CMJ was largely correlated with V-IFT (r = 0.631 to r = 0.650) while presenting small correlations with ASR (r = 0.227 to r = 0.232). Both V-IFT and ASR had moderate (r = 0.3 to r = 0.5) correlations with sprinting time at different distances and very large correlations with MSS (r = 0.797 to r = 0.866). The COD time was largely correlated with V-IFT (r = 0.765 and r = 0.775) while exhibiting small-to-moderate correlations with ASR (r = -0.279 and r = -0.301). In conclusion, it was found that locomotor performance at 30-15 V-IFT presents high levels of correlation with anthropometry and physical fitness; ASR also presents correlations with these variables, but they are smaller. This suggest that ASR is an independent variable that should be considered for inclusion in information for characterizing players' capacities.