Accelerometry is a crucial tool in basketball for quantifying the external load borne by players in response to the demands of intermittent high-intensity sports. To advance scientific knowledge in this field, it is imperative to study accelerometry across various populations, sexes, and competitive levels. The primary objective of this research was to characterize the acceleration (ACC) and deceleration (DEC) profiles of male under-18 basketball players during official games, identifying differences in acceleration and deceleration thresholds during playing periods and specific positions. Additionally, the interaction between specific positions and playing periods in acceleration thresholds was examined. Acceleration and deceleration were characterized using four variables: maximum ACC and DEC, distance covered, initial velocity and final velocity. These parameters were analyzed to understand the response of players participating in the Euroleague Basketball based on playing position and game period. A one-way ANOVA, along with effect size, was employed for statistical analysis. Demands exceeding ACC and DEC > 4 m·s−2 were found to differentiate player interventions. High-intensity ACC was greater in the first period compared to the third and fourth periods. Distinctions were observed between Guards and Forwards concerning high-intensity ACC being superior to the Centers, and Guards differed from Centers in moderate DEC (2–4 m·s−2), presenting higher values. For all playing positions, high-intensity accelerations were greater during the first period compared to subsequent periods. The four variables used for characterizing ACC and DEC were found to be interrelated. Distance covered depended on maximum ACC and DEC, initial velocity on covered distance, and final velocity on maximum ACC and DEC, distance, and initial velocity.