This is a charade combined with an anagram - one part is a straightforward synonym, while another part involves rearranging letters as indicated by a mixing word.
Start with a word meaning 'simpleton' (3 letters). Then 'broken' is your anagram indicator - rearrange the letters of 'leg he' to get the remaining letters. The definition relates to someone who can't do magic.
Answer: MUGGLE | MUG (simpleton) + anagram of 'leg he' (LEG*HE = GGLE). A Muggle is a non-magical person in the Harry Potter world who cannot perform magic.