Is like a protective helmet for the brain a phrase or clause

answer: inference

explanation:

an inference can be understood as a conclusion to which a person is able to get based on reasoning. it is the same as a deduction, a guess, an assumption.   in the sentence presented, the conjunction "but" gives the readers an idea of contrast, and, therefore, allows them to induce that despite the opponent's characteristics, andrea had something different that made her win.