Costochondritis: This condition, also known as chest wall pain syndrome, is characterized by sharp pains in the chest due to inflammation of the cartilage that connects the ribs to the breastbone. It is common in adolescents and can be exacerbated by physical activity, making it a plausible explanation for the patient's symptoms during exertion.

Musculoskeletal Strain: Given the patient's athletic background, a strain or pull in the muscles of the chest wall or between the ribs could cause sharp pains, especially during physical exertion.
Exercise-Induced Asthma: Although typically presenting with wheezing, cough, and shortness of breath, some individuals with exercise-induced asthma may experience chest tightness or pain that could be perceived as sharp.
Gastroesophageal Reflux Disease (GERD): GERD can cause chest pain that may be sharp, especially if it occurs during or after eating, and can be exacerbated by lying down or bending over, but less commonly directly associated with physical exertion.

Myocardial Infarction (MI) or Cardiac Ischemia: Although rare in a 16-year-old, cardiac issues such as MI or ischemia can present with chest pain during exertion. It's crucial to consider, especially if there's a family history of early cardiovascular disease.
Pulmonary Embolism (PE): A blood clot in the lungs can cause sudden, sharp chest pain that worsens with deep breathing or exertion. While less common in young athletes, it's a critical diagnosis not to miss, especially if there's a history of recent immobilization, surgery, or genetic predisposition to clotting.
Aortic Dissection: An emergency condition where there is a tear in the aorta's inner layer, which can cause severe, sharp chest pain. It's rare but critical to diagnose promptly.

Pneumothorax: A collapsed lung can cause sharp chest pain that worsens with deep breathing or coughing. It's more common in tall, thin males but can occur in anyone, especially with a history of lung disease.
Pericarditis: Inflammation of the sac surrounding the heart can cause sharp chest pain that may improve with sitting up and leaning forward. It's less common and might be associated with viral infections or autoimmune conditions.
Spontaneous Coronary Artery Dissection (SCAD): A rare condition where there is a tear in the coronary artery, which can cause a heart attack. It's more common in women and can be associated with exertion.