Last time I spanked my daughter was when she was maybe 7. Her and her younger brother (around 2-ish) were outside having ice cream on the picnic table. He was standing on it while she was sitting. I guess he was bugging her because she gave him a shove. For a split second he was teetering on the edge and she reached up and gave him another shove so he'd fall off. He was crying but ok - could have easily busted and arm or dislocated a shoulder.
That was so over the top bad that she got a few whacks and was sent to her room. By dinnertime everything was fine and she kept apologizing to Mike.
FTR: I was beaten regularly as a kid. Like pretty badly in some really nasty ways. And you can attest to how perfectly I survived it.