Attendees began marching toward the venue about 2 p.m. Clashes between protesters and Spencer's supporters started about an hour-and-a-half later. In addition to MSU police, other members of law enforcement with the Michigan State Police, East Lansing Police, Ingham County Sheriff and Clinton County Sheriff were on scene.
Between 12 and 24 people were arrested for a range of felony and misdemeanor offenses, including weapons violations and hindering and obstructing police, said MSU Police Capt. Doug Monette.
"The safety and security of our campus community remains our top priority", Monette said.
The university originally planned to charge Spencer's National Policy Institute group $2,000 to set aside a room on campus for the speech, but made a decision to deny the group the opportunity to speak citing safety concerns. An Okemos resident and MSU graduate, he said he just wants to voice his concerns about Spencer's appearance.
Katie Kuhn of Lansing led some anti-Spencer chants.
About 20 Spencer supporters attempted to walk directly through the crowd, inciting physical confrontations after both groups shouted obscenities at each other, Detroit Free Press reported.
Spencer popularized the term "alt-right" to refer to a fringe movement that's a mix of white nationalist and anti-Semitic beliefs.
He said an aid of his was attacked and injured by counter-protesters. Police say there were around two dozen of them who met by the hundreds of protesters. "We chased them away".
Spencer's speech was not well-attended, and he barred television cameras from recording.
50 people heard Spencer speak.