C. F. Keil and Franz Delitzsch on Deuteronomy 25:2

Deu 25:2

If the guilty man was sentenced to stripes, he was to receive his punishment in the presence of the judge, and not more than forty stripes, that he might not become contemptible in the eyes of the people. הכּות בּן, son of stripes, i.e., a man liable to stripes, like son (child) of death, in 1Sa 20:31. “According to the need of his crime in number,” i.e., as many stripes as his crime deserved.