Here’s an excerpt from a digital commentary about Ehud:
Judges chapter 3:12-14
Israel was subjugated by Eglon, the king of Moab, for eighteen years.
Judges chapter 3:15-30
The military leader whom God gave to Israel at this time was Ehud, . . . a left-handed man of the tribe of Benjamin. He was commissioned by the people to take a gift as tribute to King Eglon. He also hid a double-edged . . . dagger . . . under his clothes. After the gift had been delivered, the king probably felt at ease concerning the attitude of his Jewish subjects. Then Ehud asked for a private audience to discuss a secret message. When all the attendants had been sent away, Ehud assassinated the king and fled. By the time the deed was discovered, Ehud had assembled the men of Israel, marched against Moab, and killed about ten thousand retreating soldiers. Israel then enjoyed rest for eighty years.
I hope you have found this helpful.