Spanking a child is absolutely violence. It's just been a socially acceptable form of violence for millennia, just like some killing (either in wars or e.g. with a death penalty) has been socially acceptable for as long.

The question isn't, "is spanking violence?"

It's "are norms changing around whether spanking is socially acceptable?"

And now, for a lot of people, no, it isn't. Hitting a child to punish them is no longer "the basics" for a lot of people, even if it's how a lot of the older generation grew up and took for granted.

I have no kids, but most of my peers do now, and spanking is sooooo much off the table, it's on par with overt racism (saying the n-word, saying discrimination is okay, etc). Absolute social taboo, and absolutely no question that it's "physical violence".