Mercatus Center Director Tyler Cowen suffered a pepper-spray attack at the hands of a deranged man on Wednesday at George Mason University, where he teaches economics.

According to ArlNow.com, a white man in his 20s or 30s intruded on Cowen’s 3 p.m. class, declaring that he was placing the author under a citizen’s arrest. Cowen asked him to leave — and in the ensuing brouhaha, the man pepper-sprayed Cowen right in the face.

Arlington police arrested the man shortly afterwards, after an off-duty officer heard the fight — and a GMU student subdued the suspect as he tried to escape the scene.

Arlington County Police spokesman Dustin Sternbeck said Cowen didn’t know the man. Paramedics treated Cowen and a dozen other students affected by the pepper spray at the scene.

Cowen played off the ordeal on Twitter, joking that he was headed back to work as if nothing had happened.

Back to work! (as usual)… — tylercowen (@tylercowen) March 26, 2014

How the suspect so easily gained access to Cowen’s classroom is unclear.

This story is developing.

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