Er verletzt sie mehr als sie ihn.
"Er" is a nominative "he" (subject) at the beginning of the sentence followed by the conjugated verb. The first "sie" is "her" (accusative pronoun) followed by "mehr als" meaning "more than". In German, you don't need something equivalent to "does" and you don't need the preposition "to"here, instead, you just say something like "more than she him". Both "sie" and "ihn" at the end of the sentence are accusative. German native speakers perfectly understand which pronoun refers to whom in this sentence.
