“It came to pass when Gideon died.” This starts another section of Judges, after Gideon died. It would have been helpful to start chapter 9 with this verse.
“the children of Israel turned back.” (cp. Judges 2:19).
“Baal-berith.” More literally, “Baal of the Covenant.” It likely means that the people who worshipped this Baal made a covenant with him, or the local people made a covenant with him. Of course, this is a direct insult to God, who had made a covenant with Israel (Exod. 24).