This can vary from mild concussion to severe diffuse headinjuries with bleeding on the brain.
The topic of concussion is vast and controversial and the website is not the platform to go into such detail. As a rule of thumb patients should not return to play when symptomati. Complete rest from all activities (not only contact) is advised until cerebral autoregulation is corrected.
A diffuse axonal injury DAI) happens when there is microscopic tears in the white matter tracts in the brain. This follows high impact injuries. Prognosis varies on the degree. High grade DAI can remain in a permanent vegetative state. Surgery is not indicated for DAI.
Traumatic bleeding on the brain can either be outside (extradural hematoma) the dura (brain membrane) or inside the dura (subdural hematoma) This type of injury can be operated on by draining the blood by performing a craniotomy.