Charles Ellicott Commentary Judges 9:43

"And he took the people, and divided them into three companies, and laid wait in the field; and he looked, and, behold, the people came forth out of the city; And he rose up against them, and smote them." — Judges 9:43 (ASV)

Into three companies. —Why he only made three companies this time can only be matter of conjecture.

He rose up against them, and smote them. —He was evidently a man of ruthlessly vindictive temperament, for these people whom he killed were mere farmers, not an armed force.