en_tn/1sa/18/10.md

a harmful spirit from God

Here "harmful spirit" may refer to either "a spirit that causes trouble" or "an evil spirit." See how you translated this in 1 Samuel 16:15.

a harmful spirit from God rushed upon Saul

The phrase "rushed upon" means the harmful spirit influenced Saul. In this case it means it caused Saul to be troubled and act crazy. See how you translated a similar phrase in 1 Samuel 10:6.

he prophesied

"a spirit caused him to speak." Here it appears that what Saul said was of no benefit to the hearers, so some modern English versions read, "he spoke words that made no sense."