The motivation of an athlete is determinant for the athletic engagement of the adolescent. The present study attempts to analyze the motivation of adolescent basketball and football players from the perspectives of Achievement Goal Theory (Nicholls, 1989) and Self-Determination Theory (Deci & Ryan, 1985). The study's sample was composed of 248 athletes from 12 to 17 years of age. Half were from basketball and half were from football. The instruments that were utilized were: the Spanish version of the Sport Motivation Scale (SMS) (Núñez, Martín-Albo, Navarro, & González, 2006), the Spanish version of the Perceived Motivational Climate in Sport Questionnaire-2 (PMSCQ-2) (Balaguer, Mayo, Atienza, & Duda, 1997), and the adapted Spanish translation (Moreno, Moreno, & Cervelló, 2007) of the Intention to be Physically Active Scale (IPAS) by Hein, Müür, and Koka (2004). The comparison of the means of the variables between football and basketball players was done utilizing the student t-test for independent samples. Significant differences were found for variables such as: intrinsic motivation (IM) toward accomplishment, external regulation, amotivation, task, ego, and Self-Determination Index (SDI). Basketball players obtained higher values in the SDI, in task, and in IM toward accomplishment than football players. The search for premature performance in football and coaches' educations can help to explain these differences. The importance of these differences reside in the relationship between these motivational variables and the adherence to athletic practice. In conclusion, basketball demonstrated better values in motivational variables, which demonstrates that training sessions are more oriented toward task than ego, that players have more intrinsic and self-determined motivation, and therefore, the adherence of the young athletes will be greater in this sport
