It gets so quiet during the second movement of the Brahms Symphony No. 2, you could almost hear a pin drop. Or a sneeze. Or a fist hitting a face. Such was the case Thursday night at Orchestra Hall in a ruckus the Chicago Symphony Orchestra officially described as “an incident” between “two patrons.” But shocked concert-goers and police called it a fist fight in one of the boxes — where the elite typically sit and expect a more refined experience. Just as the second movement was drawing to a gentle close — with Music Director Riccardo Muti at the...