One of the functions of the Shamgar narrative of one verse (Judges 3:31) was to effectively push the pause button, to give the reader a chance to catch our breath before plunging forward again. The brief interlude between the accounts of Abimelech and Jephthah serves the same purpose.
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1 After Abimelech there arose to save Israel Tola the son of Puah, son of Dodo, a man of Issachar, and he lived at Shamir in the hill country of Ephraim.