Concussion: The development of a headache 24 hours after a bump on the head, especially in the context of athletic activity, strongly suggests a concussion. Concussions can present with delayed symptoms, and the mechanism of injury (a bump on the head) is consistent with this diagnosis.

Migraine or Tension Headache: These could be triggered by the initial trauma or by other factors unrelated to the injury. The delay in onset and the absence of immediate symptoms could fit with these diagnoses, especially if the patient has a history of headaches.
Exertional Headache: This type of headache is related to physical activity and could be exacerbated by the athletic practice the next day, independent of the initial head bump.

Subdural Hematoma or Epidural Hematoma: Although less likely, these conditions can present with delayed symptoms after a head injury. They are medical emergencies requiring immediate attention. The mechanism of injury and the delay in symptom onset make it crucial not to miss these diagnoses.
Subarachnoid Hemorrhage: This is another serious condition that could present with a delayed headache after head trauma. It requires prompt diagnosis and treatment.

Arteriovenous Malformation (AVM) or Aneurysm: These vascular abnormalities could potentially cause a headache after minor trauma due to bleeding or rupture. They are rare but critical to diagnose due to their potential for severe consequences.
Infection (e.g., Meningitis): Although unlikely to be directly related to the head bump, if the patient had been exposed to infectious agents, the headache could be a symptom of an underlying infection. This would be more likely if accompanied by other symptoms such as fever, stiff neck, or rash.