Struck is the past tense of strike, which means (1) To hit forcibly and deliberately with one's hand or a weapon or other implement, or (2) to occur suddenly and have harmful or damaging effects.   I think the author of this story was being a bit over-dramatic in describing what happened to Cravalho.  The silk flag may have touched the back of her head, but to report that she was “struck” by the flag is a very long stretch.  It did occur at the Oscars where drama and dramatics are everything, so I guess it is ok.