You can't help but root for the banished underdog who becomes the leader of his people. Jephthah lives in exile with a band of misfits, outcasts, and merry men, far from the civilized company of his half-brothers (11:1-3). But when Israel finds itself in need of a mighty soldier, they turn to him, and he delivers big-time, though it costs him dearly in the end.
Jephthah swears that if the Lord gives him victory, he'll sacrifice on the Lord's altar anything that approaches him at the gate upon his return home. "And Jephthah made a vow to the Lord, and said, 'If you will give the Ammonites into my hand, then whoever comes out of the doors of my house to meet me, when I return victorious from the Ammonites, shall be the Lord's, to be offered up by me as a burnt-offering'" (11:30-31). The battle won, Jeph resolves to keep his promise. It takes a stand-up guy to keep his word no matter what, which makes it all the more heartbreaking when Jephthah finds himself honor-bound to kill his only daughter: "Then Jephthah came to his home […] and there was his daughter coming out to meet him […] When he saw her, he tore his clothes, and said, 'Alas, my daughter! […] I have opened my mouth to the Lord, and I cannot take back my vow'" (11:34-35). His daughter, for her part, is a real trooper and goes along with this whole thing without protest (11:36-39). This sort of echoes the Abraham and Isaac story, only without the angelic happy ending. That's because, don't forget, this is Judges: Happy endings are for sissies.