This study aims to examine the effects of early offensive player substitution on the outcome of the match and player psychology in professional football matches. The method of the research is the simultaneous mixed methods research design in which quantitative and qualitative methods are used together. In the quantitative part, 345 offensive substitutions made by the teams in the early phase (during the first half or the halftime), given that the match was a draw or a loss for their side, in a total of 612 games played in the 2017-2018 and 2018-2019 seasons at the TFF 1st League were examined. In the qualitative part four coaches who made early-stage offensive substitutions in case of a draw or loss, four offensive players entering the game and four players leaving the game during the same seasons were interviewed. The data gathered for the quantitative part was analysed using chi-square test and a content analysis was performed for the qualitative part using a semi-structured interview form. As a result of the research, it was determined that the coaches generally associated early stage offensive substitutions they made with the score of the match and saw the inclusion of offensive players in the game as an effort to produce a score. However, it has been determined that 15.07% of the players contribute (goals and/or assists) and 84.93% do not contribute after substitutions made in case of draw or loss in the relevant seasons. Offensive players entering the game listed the factors that negatively affect their ideal performance as lack of motivation, inability to concentrate, pressure felt, insufficient warm-up, inability to adapt to the pace of the game. In addition to this, it was determined that the team gained points in the competitions in which the players contributed, and there was no change in the team’s score in the competitions in which the players did not contribute was statistically significant (p<0.05). Players who were removed from the game with early-stage offensive substitutions assert that they face both psychological and social problems. Especially being removed from the game in the first half was described as a worse experience by the players. Moreover, players leaving the game asserted that their performance was adversely affected during the training sessions and in the upcoming competitions after the match they were substituted as they experienced loss of self-confidence, feeling worthlessness, loss of confidence in their coach, fear of making mistakes, avoiding taking responsibility, anxiety about being exposed to the same change again and not being able to focus. As a result, considering the multidimensional effects of early-stage offensive substitutions on both the outcome of the match and the players, it is considered that it would be more beneficial for coaches to make such changes by evaluating not only score-based changes but also other dynamics regarding the game.