This study investigated how pitch size and a task type (position vs. possession games) influence running demands and external load across player positions in soccer training. Twenty-five young professional soccer players (21.9 ± 1.9 years) participated in 36 training sessions during the 2021–2022 season. Position and possession games were conducted on three pitch sizes (small, medium, large). Players wore GPS devices to measure total distance covered (DC), peak speed, and acceleration/deceleration metrics (low-intensity < ±3 m·s⁻² and high-intensity > ±3 m·s⁻²). Mixed models assessed the effects of pitch size and a task type on these metrics and positional differences. Possession games elicited higher total DC than position games across all sizes studied (p < 0.005). In the large format, the peak speed was higher in possession than in position games (p < 0.001). On small pitches, possession games resulted in greater low-intensity accelerations/decelerations (ACC<3/DEC<3), but fewer high-intensity accelerations/decelerations (ACC>3/DEC>3) and maximal deceleration compared to position games (p < 0.05). Positional analysis revealed that central defenders and fullbacks reached greater total DC across all three formats of possession games (p < 0.05). Central-midfielders and forwards recorded higher peak speeds in the large possession game (p ≤ 0.01). Wide-midfielders achieved fewer ACC<3 and DEC<3 events in position games during the small format, while fullbacks performed fewer ACC<3 but more ACC>3 in the same format during position games (p ≤ 0.05). Field size and the game format significantly affect external load in soccer. Possession games require greater total DC regardless of size and higher peak speeds on larger fields, while position games involve more high-intensity actions, reflecting players’ tactical roles.