Commotio Cordis: This is a condition caused by a blunt impact to the chest, which can lead to cardiac arrest. Given the context of a football tackle, this diagnosis is highly plausible due to the direct trauma to the chest.

Myocardial Contusion: A blunt trauma to the chest, such as from a football tackle, can cause a myocardial contusion, leading to ST elevation on an ECG.
Hypertrophic Cardiomyopathy (HCM): Although less directly related to the immediate cause of a football tackle, HCM is a common cause of sudden cardiac death in young athletes and can present with ST elevation.

Acute Myocardial Infarction (MI): Although rare in teenagers, an MI could present with ST elevation and must be considered, especially if there are risk factors or a family history of early cardiovascular disease.
Pulmonary Embolism (PE): While less common in this demographic, a PE can cause ST elevation in certain leads and is a potentially life-threatening condition that requires immediate attention.
Aortic Dissection: This is a rare but critical condition that could potentially occur after a severe chest trauma, presenting with ST elevation among other symptoms.

Myopericarditis: Inflammation of the myocardium and pericardium can cause ST elevation and could be considered if there's a history of recent infection or autoimmune conditions.
Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC): A rare condition that affects the right ventricle and can lead to sudden cardiac death, presenting with various ECG abnormalities including ST elevation in some cases.
Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT): A rare genetic disorder that can cause life-threatening arrhythmias during physical activity or emotional stress, potentially presenting with ST elevation during episodes.