Our research uses GPAI (Game Performance Assessment Instrument) as a method to assess the game performance of basketball players. Using actual games as our object of analysis, we tried to assess the players' performance. The results of the research of GPAI assessment of game performance: we were able to discover the players' problem areas and also reconfirm their strong points. The assessment not only included the total results of the visible performance centered on the ball, but also included results where the viewpoint was focused on assessing the inherent invisible aspects of the game too. We were able to achieve deeper insight in our assessment.