After Gaal's expulsion, "the people went out into the field," either to complete the vintage, or for some other agricultural operation. "They" (Zebul and his party) sent word of this to Abimelech.

And it came to pass on the morrow,.... The day after the battle:

that the people went out into the field; some think to fight, and try the event of another battle, in order to be freed from Abimelech, but that seems not so likely: rather to finish their vintage, as Josephus (l), or to till their ground, to plough and sow, which quickly came on after the vintage was ended; find this they might do the more securely, since Abimelech had withdrawn himself and his forces to his place of habitation, and so concluded he would not soon at least return to them; and the rather they might think he would be more easy, with then, since Gaal was thrust out from among them:

and they told Abimelech; or it was told Abimelech, that the people came out into the field, and so an opportunity offered to him to come and cut them off, as they were at their business unarmed.

(l) Antiqu. l. 5. c. 7. sect. 4.

The next day the people of Shechem went into the field, apparently not to make war upon Abimelech, but to work in the field, possibly to continue the vintage. But when Abimelech was informed of it, he divided the people, i.e., his own men, into three companies, which he placed in ambush in the field, and then fell upon the Shechemites when they had come out of the city, and slew them.

And it came to pass on the morrow, that the people went out into the field; and they told Abimelech.

9:42 Went out - to their usual employments about their land.

9:30-49 Abimelech intended to punish the Schechemites for slighting him now, but God punished them for their serving him formerly in the murder of Gideon's sons. When God uses men as instruments in his hand to do his work, he means one thing, and they another. That, which they hoped would have been for their welfare, proved a snare and a trap, as those will certainly find, who run to idols for shelter; such will prove a refuge of lies.