“will strike the back.” The Hebrew text does not have the verb, so it has to be supplied from the culture. Thus, some versions have “is for,” or “is in store,” or a similar phrase. People who behaved foolishly were sometimes beaten with a rod, or hit, struck, poked or tapped with it, depending on the person and the situation.
It was a common custom for men to carry a walking stick, a “rod,” that they would use for support on the rough ground and for self-defense (even against snakes and scorpions), and so it was always handy and easy to use, and they would use it to correct people if the situation warranted. Misbehaving or disobedient slaves (Exod. 21:20-21) and children (Prov. 13:24; 22:15; 23:13-14; 29:15) were commonly corrected with the rod (cp “fools,” Prov. 26:3). Because the physical rod was commonly used for correction, the word “rod” became used figuratively for correction in general even though an actual “rod” was not used (2 Sam. 7:14; Job 21:9). That the “rod” was used figuratively for correction that came in other ways besides the actual rod means that we have to pay attention to verses such as Proverbs 22:15 where the word “rod” can have both the meaning of a physical rod and correction in some other way as well.
The correction of children, while done from love and concern, was generally much harsher in biblical times than it is today, and that stemmed from the fact that medical care was primitive at best. Injuries that would be considered minor today, such as cut or broken bone, could mean the life of the child.
Our society has in large part moved away from the idea of stern correction, but there is no evidence that we are better off for it. Quite the contrary. If the way students behave in school is any indicator at all, the absence of stern correction is deleterious to people. We should note that God, who created people and knows us better than we know ourselves, advises stern correction to put an end to foolishness.