First of all, I won't visit a site called "legalinsurrection.com."
But I will answer the titular question independent of anything said on that site.
No injury is required before one can legally defend himself. It will vary from State to State, the particulars of a situation that gives rise to lawful self-defense. However, I know of no State that requires actual injury before one may defend himself. There may be such a State law somewhere, but that would be an irresponsible law. I would not live in such a State that does not recognize my right to defend myself from what a reasonable man would see as an imminent threat to life or limb.