His calling upon the Lord sounds orthodox, pious. The only question is whether he actually trusts in the Lord to vindicate his people. Or is he more motivated by self-interest? We must also keep in mind that from the Lord’s side, he had not yet committed to doing anything for Israel. In fact, the last time we heard from the Lord, he was out of patience with Israel (Judges 10:16).
27 I therefore have not sinned against you, and you do me wrong by making war on me. The LORD, the Judge, decide this day between the people of Israel and the people of Ammon.”