Albert Barnes Commentary 1 Samuel 14:33

"Then they told Saul, saying, Behold, the people sin against Jehovah, in that they eat with the blood. And he said, ye have dealt treacherously: roll a great stone unto me this day." — 1 Samuel 14:33 (ASV)

Sin against the Lord - The prohibition was older than the Law of Moses (Genesis 9:4). Compare Acts 15:20 and 15:29.