Thirty people were injured Saturday night in a stampede in the mosh pit of a rock concert at RFK Memorial Stadium. D.C. Fire Department spokesman Alan Etter said one of the injured went into cardiac arrest and was taken to a hospital. Paramedics were treating other concertgoers for bruises and broken bones. THE INCIDENT occurred at about 8 p.m. ET at the WHFS music festival, an event sponsored by a local radio station. Etter said earlier reports that the stadium’s bleachers had collapsed were inaccurate. Ambulances from Montgomery and Prince George’s Counties responded to the scene and were assisting fire...