The word that the elders of Gilead use here for leader
(קָצִין) is different than the one in Judges 10:18 (רֹאשׁ). The elders had promised headship over all the inhabitants of Gilead to anyone who would volunteer to lead them in battle. Here they offer the position of military leader (Joshua 10:24; Isaiah 22:3; Daniel 11:18). Though desperate, the elders are careful to offer Jephthah a lesser role than they had made available to full citizens of Gilead.1 They are trying to get him on the cheap.2 Maybe they thought the outcast will be flattered and jump at the chance of moving up on the social ladder.
6 And they said to Jephthah, “Come and be our leader, that we may fight against the Ammonites.”