Cervical Strain or Sprain: This is the most common injury in football tackles, resulting from overstretching or tearing of the neck muscles and ligaments. The presentation of neck pain, refusal to move the neck, and tenderness at C5 is consistent with this diagnosis.

Cervical Disc Herniation: A possible injury from the tackle, which could cause pain and tenderness, especially if the disc herniation is compressing a nerve root, such as at the C5 level.
Stinger or Burner: A common injury in contact sports, characterized by a burning pain or stinging sensation in one arm, which could be related to the mechanism of injury and the presence of neck pain and tenderness.

Cervical Spine Fracture: Although less likely, a fracture could occur from a significant impact, such as a football tackle. Missing this diagnosis could lead to serious complications, including spinal cord injury.
Spinal Cord Injury: Any injury that affects the spinal cord could have severe and permanent consequences, making it crucial to consider and rule out, especially with symptoms like neck pain and refusal to move.
Epidural Hematoma: A rare but potentially life-threatening condition where bleeding occurs outside the dura mater, which could compress the spinal cord and lead to neurological deficits.

Cervical Ligamentous Injury: While possible, pure ligamentous injuries without fracture are less common in children due to the greater elasticity of their ligaments and bones.
Osteochondrosis (e.g., Scheuermann's disease): A condition affecting the growth plates in the spine, which could cause neck pain but is less directly related to an acute traumatic event like a football tackle.
Infectious or Inflammatory Causes: Conditions like discitis or osteomyelitis could cause neck pain and tenderness but are less likely in the context of an acute traumatic injury.