Peel Regional Police Sgt. Matt Small says the man was detained on Thursday evening under the mental health act after trying to force his way onto an airplane.
Small did not provide details on the man's identity or which aircraft he was trying to board, but says the man wasn't injured in the incident.
Small says the man was carrying a briefcase that he refused to put down, prompting officers to fire one blast from a Taser.
A bystander captured some footage of the incident on a video that was later posted to YouTube.
The footage shows the man was standing still while the video was being shot, but Small says he was showing more signs of agitation before the camera started rolling.
"My understanding is that he was a bit more aggressive," Small said in a telephone interview. "He was being loud, and that's what actually caused our attendance. People were concerned."
Deploying a Taser to subdue the man seemed like the safest course of action for all concerned at the time, he added.
The YouTube video of the incident, filmed at Pearson's Terminal 1, shows officers surrounding the man as he stands holding a briefcase. One officer has a Taser aimed at the man's chest.
Police repeatedly ask the man to drop the briefcase, then the sound of a bang is heard.
The man screams, shakes and slumps forward to the ground where other officers handcuff his arms behind his back.
The man's name has not been released, nor have police indicated where he is from.
It is unclear what flight he was attempting to board, but the YouTube video, uploaded by user Vinay Saini, says the man was trying to "forcefully board" a Turkish Airlines flight.
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