Possible meanings are 1) "the leaders among the descendants of Dan will judge their people" or 2) "The descendants of Dan will judge the people of Israel." (See: [[rc://en/ta/man/translate/figs-metonymy]])
"Dan will be like a snake beside the road." Though a snake is small, it but can bring down a rider off his house, so is Dan, though a small tribe, is very dangerous to its enemies. (See [[rc://en/ta/man/translate/figs-metaphor]])