The aim of this research was to examine the influence of two variables, the type of marking (with or without man-marking) and the number of players per team (3, 6, or 9) on the physical and physiological demands of sided games in soccer. Eighteen amateur players were monitored with GPS and heart rate devices. The following variables were analyzed: a maximum heart rate, a mean heart rate, time spent in each intensity range, total distance covered and distance covered in different speed ranges, a player load, maximum speed reached, and a work:rest ratio. The results showed that the type of marking influenced the physical demands of players, with greater total distance, a player load and a work:rest ratio when man-marking was used in the 3 vs. 3 (737 m, 95 Arbitrary Units (AU) and 3.4 AU, respectively) and 6 vs. 6 (783 m, 95 AU and 5.3 AU, respectively) games (p<0.05). The number of players also had an effect on physiological intensity, with more time being spent at the <80%HRmax during the 9 vs. 9 and 6 vs. 6 games (more than 30%) compared with the 3 vs. 3 format (less than 15%) (p<0.05). These findings could help coaches to understand how the modification of different variables in sided games influences the physical and physiological demands of players.