The anterior band of the medial collateral ligament (MCL) is an important stabilizer for valgus stress at the elbow. When practised intensively and repetitively, activities using overhead throwing motions can injure this ligament and its insertion. If these activities occur when the epiphyses are not yet fully fused, traction forces can result in bony detachments in the area of the MCL insertion. This study was based on commingled graves found in 16 Middle and Late Neolithic caves from Belgium. We recorded the presence of MCL lesions on 196 humeri and studied the relation between lesions, siding, and robusticity. 5.1% of the humeri displayed MCL lesions, which affected only the right robust humeri. Our results suggest a social division in throwing activities in Belgium during the Neolithic. They also suggest that throwing practice started from a young age, which invites us to re-examine the role of teenagers in prehistoric societies.