See discussion. Hitting your head won't cause a stroke in the way we generally refer to a stroke-a blockage of a blood vessel in your brain. However hitting your head hard can do some other things that aren't good. A more likely effect would be a concussion, which can have neurological effects on you. Less likely, but a hard hit could potentially cause a bleed in your brain, & this could have stroke-like effects.
Yes but rarely. Most likely hitting your head hard enough to cause internal damage, i.e. Within the skull cavity, will result in bruising of brain tissue, subdural hematoma, extradural hematoma, and intracerebral hematoma. These are not properly called strokes. The only way a stroke could occur would by loosening of a plaque from an arterial wall or compression of a carotid artery in the neck.