The sequence of events that led to the death of an Emerson College student began when a half-dozen officers on horseback were surrounded by rioting Red Sox fans on Lansdowne Street about 1:30 a.m. yesterday, witnesses said. By the time armor-clad cops dispersed the crowd of some 3,000 in the shadow of Fenway Park's Green Monster, Victoria Snelgrove, 21, lay fatally injured. She had been struck in the eye by one of a number of pepper balls fired by police to quell unruly fans throwing bottles and bricks. ``The cops (on horseback) pushed in and the people closed in behind...