Subungual hematoma: This condition is characterized by bruising under the toenail, often caused by trauma, but can also occur spontaneously or due to repetitive stress, such as playing football. The location at the base of the toenail and the onset after physical activity without a specific injury make this a plausible diagnosis.

Contusion or bruising of the toe: Direct trauma to the toe, even if not remembered, could cause bruising. The absence of a recalled injury does not rule out minor trauma, especially in a contact sport.
Peripheral nerve entrapment or irritation: Sensitivity up the medial leg to the medial groin could indicate irritation of a peripheral nerve, such as the saphenous nerve, which runs along the medial aspect of the leg and could be irritated by physical activity.
Shin splints or medial tibial stress syndrome: While typically causing pain rather than sensitivity, shin splints could potentially cause referred sensations up the leg and might be associated with bruising if there was significant trauma to the muscle or bone.

Deep vein thrombosis (DVT): Although less common in young, otherwise healthy individuals, DVT can cause leg swelling, pain, and sensitivity. It's a critical diagnosis to consider due to the risk of pulmonary embolism.
Compartment syndrome: This is a serious condition that can occur after trauma or intense physical activity, leading to increased pressure within the muscle compartments of the leg. It can cause pain, swelling, and sensory changes.
Osteonecrosis or stress fracture: These conditions can cause pain and potentially bruising if there is an associated fracture. They might not be immediately suspected without specific imaging but are important to consider, especially with activity-related onset.

Vasculitis: Inflammation of the blood vessels can cause a variety of symptoms, including bruising and sensitivity. However, it would be an uncommon cause of these specific symptoms without other systemic signs.
Neurological disorders: Certain neurological conditions, such as neuropathies, could potentially cause sensitivity up the leg. These would be less likely without other neurological symptoms or a history suggestive of a neurological condition.
Infection: Although rare, infections such as cellulitis or abscesses could cause redness, swelling, and sensitivity. Typically, there would be other signs such as fever, redness, or warmth of the skin.