This study aims to: i) describe the objective (area occupied by the team, AOT) and subjective (spatial perception of the occupied area, SPOS) tactical demands, ii) identify the inter-subject variability and the relationship between AOT and SPOS, and iii) compare the demands between offensive and defensive phases, during small-sided games. Twelve semi-professional football players were tracked using WIMU PRO® inertial devices. The results indicated an AOT (attack=257.6±60.6; defense=120.3±37.8 m2) and SPOS (attack=3.5±0.7; 2.7±0.6 arb. unit). Differences were found between attack and defense phases in both variables (p>0.001; AOT, d=2.72; SPOS, d=1.23), as well as a strong relationship between both indicators (r=0.92). In conclusion, the variables AOT and SPOS discriminated the effect of the game phase and the training day. Future research with a larger sample is necessary to confirm the validity of the PSOS.