Answer: I would contend that the right answer is the B) Players often return to a game after a head injury—they.
Explanation: By using a dash or specifically an "em-dash" ( — ) at the end of the sentence, the writer is clarifying or amplifying the information that he or she has already provided (that players often return to a game after a head injury). Options C and D are grammatically incorrect, so they should be discarded. Furthermore, since the two sentences ("players..." and "they do not want...") are not independent, the use of a semicolon (option A) should also be discarded.
