This work studied if decision-making differences between girls and boys existed in different versions of the traditional game called la pelota sentada according to their roles, sub-roles (decisions), valence (cooperation or opposition) and level of adjustment (effectiveness) of motor behaviours. One hundred and twelve compulsory secondary education and further education pupils took part in the study. The age range was 12 to 17 years (M = 14.2; SD = 2.2). The observational design was nomothetic, one-time and multidimensional. A mixed system of registration "ad hoc" was designed. Univariate analyses were performed using contingency tables, and for multivariate analysis the CHAID classification tree statistical technique was used. The study enabled us to assess the effectiveness of the players' motor behaviour types and to expose a system of asymmetrical motor relationships underlying the superficial view of a motor game. The study verified decisions, asymmetric motor relations and different effectiveness in the behaviour of girls and boys.