Can you get glaucoma from hitting the back of your head?

Typically no. Posterior blunt head trauma can cause optic nerve injury and lead to poor vision, but glaucoma refers to eye conditions involving eye pressures that are causing injury to the nerve. Certainly direct trauma to an eye can result in glaucoma.
No. Usually it's trauma directly to the eye to sustain angle recession or traumatic glaucoma, i.e. Boxing.