John Gill Commentary Judges 11:32

"So Jephthah passed over unto the children of Ammon to fight against them; and Jehovah delivered them into his hand." — Judges 11:32 (ASV)

So Jephthah passed over to the children of Ammon, to fight
against them
As in (Judges 11:29) , after he had made the above vow:

and the Lord delivered them into his hands ;
when both armies met and engaged, victory was on the side of Jephthah; the Lord being with him, and giving him success, to whom all success is justly ascribed.