Morris Dees of the Southern Poverty Law Center was behind the violence that landed one college professor in the hospital and a speaker shut off from being able to speak, according to Carl Cannon, writing in RealClearPolitics.

Under different circumstances, Alabama civil rights lawyer Morris S. Dees and American Enterprise Institute scholar Charles Murray might have been colleagues, even pals. Instead, Murray found himself in a near-riot at Middlebury College after accepting a speaking invitation from Republican students at the Vermont school. Students and faculty galvanized by Dees’ political organization barred Murray from speaking. They shouted him down, chanted their own manifesto, and pulled fire alarms to prevent him from being heard.
When Murray and Middlebury professor Allison Stanger tried to leave the building, they were followed by protesters who accosted them physically. The professor was grabbed by the hair and her neck twisted—she was fitted with a neck brace at a hospital—and their car rocked in a way that alarmed local authorities.

Source: The Hate Group That Incited the Middlebury Melee | RealClearPolitics