Adam Clarke on Ruth 4:7

A man plucked off his shoe - The law of such a case is given at large in Deu 25:5-9. It was simply this: If a brother, who had married a wife, died without children, the eldest brother was to take the widow, and raise up a family to the brother deceased; and he had a right to redeem the inheritance, if it had been alienated. But if the person who had the right of redemption would not take the woman, she was to pull off his shoe and spit in his face, and he was ever after considered as a disgraced man. In the present case the shoe only is taken off, probably because the circumstances of the man were such as to render it improper for him to redeem the ground and take Ruth to his wife; and because of this reasonable excuse, the contemptuous part of the ceremony is omitted. See the note on Deu 25:9.