Abstract: The key idea of this study is to investigate the relationship between self-discipline, coach’s behaviors and teammate’s factors and aggressiveness of youth football team players. This research is a quantitative study using an experimental case study (one-shot case study) method. A total of 30 youth football players from Perlis and Kedah under 18 football team were recruited using purposive sampling, were involved in this study. Researchers used a questionnaire which consists five scale Likert point and data were analyzed using a Pearson’s correlation coefficient (r) statistical analysis to identify the correlation between selfdisciplines, coaches behaviors and teammates factors towards aggressiveness of these youth football team players by using SPSS version 20. The statistic has shown that youth football team player’s self-discipline and coaches behaviors are not the main causes of aggressiveness. Yet teammates, in Perlis and Kedah youth football team, is a leading cause or the main contributing factors of aggressiveness among footballers under the age of 18. Further work is necessary on these issues of aggressiveness.