Costochondritis: This condition, characterized by inflammation of the cartilage that connects the ribs to the breastbone, is a common cause of chest pain in adolescents, especially with sharp pain exacerbated by movement or exercise.

Musculoskeletal strain: Given the context of exercise and running, musculoskeletal strain or injury to the chest wall muscles or ribs is a plausible cause.
Asthma or exercise-induced bronchospasm: Although there's no cough mentioned, asthma or exercise-induced bronchospasm could cause chest pain or discomfort during exercise due to airway constriction.
Gastroesophageal reflux disease (GERD): GERD can cause chest pain, especially if symptoms worsen with exertion or certain food intake, though it's less directly related to exercise.

Myocardial infarction or cardiac issues: Although rare in teenagers, cardiac conditions such as myocardial infarction, hypertrophic cardiomyopathy, or other structural heart diseases can present with exertional chest pain and are critical not to miss due to their high mortality rate.
Pulmonary embolism: Though unlikely in a healthy 17-year-old without risk factors like birth control or smoking, pulmonary embolism is a life-threatening condition that must be considered, especially if there's a history of recent immobilization, trauma, or family history of clotting disorders.
Pneumothorax: Spontaneous pneumothorax can occur in tall, thin adolescents and would present with sudden onset of sharp chest pain, possibly worsening with deep breathing or movement.

Pneumomediastinum: Air leaking into the space between the lungs could cause chest pain, often associated with deep breathing or coughing, though it's less common.
Pericarditis: Inflammation of the pericardium, the sac surrounding the heart, can cause sharp chest pain that may improve with sitting up and leaning forward, though it's less likely without other symptoms like fever or recent viral illness.