Charles Ellicott Commentary Exodus 21:33

"And if a man shall open a pit, or if a man shall dig a pit and not cover it, and an ox or an ass fall therein," — Exodus 21:33 (ASV)

If a man shall open a pit. —Rather, uncover a well. The wells in the East commonly have covers, which are removed when water is drawn, and then replaced. If a man neglected to replace a cover, he was rightly answerable for any damage that might ensue. The case was the same if he dug a new well, and neglected to cover it over.