SANFORD, Fla. — The Rev. Al Sharpton, an MSNBC host and liberal political figure, riled up a mostly-black Sanford, Fla., crowd on Thursday night in the wake of the killing of 17-year-old student Trayvon Martin. “Some people said to me in the media — ‘Let me get this straight,’ they said. ‘Reverend, it seems like there’s a lot of people who are angry — are you afraid of violence?’” Sharpton preached to the central Floridian crowd. “I said, ‘No. I’m afraid of the violence you already had.’” “Violence is killing Tray Martin,” Sharpton continued. “Don’t act like we are the...