A 15-year-old boy was referred to our hospital for further investigation and treatment of sternal osteomyelitis due to blunt chest trauma, more specifically elbowing during a basketball game 19 days earlier. On an initial presentation, his chest was markedly swollen and chest computed tomography demonstrated a sternal fracture and massive fluid collection in the chest wall. Since his general condition remained fairly good, we initially selected minimal drainage concomitant with antibiotics; if it was unsuccessful, we planned to switch to a more radical debridement procedure. The patient recovered without further invasive intervention and was discharged on postoperative day 26. There is no sign of recurrence six months after operation. This case report indicates that minimal drainage would be a good option for treatment in a phased strategy.