The purpose of this study was to examine the effects of rule-based and rule-free 5v5 small-sided games played on different pitch sizes on the physical and physiological performance of young soccer players. Ten male soccer players (mean age = 16.59 ± 0.51 years) from the U16–U17 teams of a professional club voluntarily participated in the study. Each participant performed in four different small-sided game formats (rule-based small field, rule-based large field, rule-free small field, and rule-free large field). During the games, players’ physical and physiological performance variables were collected. Heart rate (mean and maximal) was analyzed as a physiological variable, while running distance (m) and running speed (km·s⁻¹) were analyzed as physical variables. A telemetric heart rate monitor (Polar V800, Polar Electro Oy, Finland) and the rating of perceived exertion scale were used as measurement tools. Data were analyzed using the SPSS 23.0 statistical package program. In addition to descriptive statistics, differences between the game formats were examined using the Wilcoxon Signed-Rank Test (p < 0.05). The results showed that pitch size and rule structure caused significant differences in heart rate, running distance, and running speed. In conclusion, pitch size and rule design play a critical role in determining the physiological load of training in small-sided games. These findings provide valuable insights for practitioners in training planning and load management and may serve as a reference for future research.