Charles Ellicott Commentary 2 Kings 17:25

"And so it was, at the beginning of their dwelling there, that they feared not Jehovah: therefore Jehovah sent lions among them, which killed some of them." — 2 Kings 17:25 (ASV)

The Lord sent (the) lions. —In the interval between the Assyrian depopulation and the re-peopling of the land, the lions indigenous to the country had multiplied naturally enough. Their ravages were understood by the colonists as a token of the wrath of the local deity on account of their neglect of his worship. The sacred writer endorses this interpretation of the incident, probably remembering Leviticus 26:22. (Ezekiel 14:15.)

Which slew. —The form of the verb implies a state of things which lasted some time. Literally, and they were killing among them.