Do yourself a favor and watch the video before you read the explanation of what the hell happened here. Trust us.
Okay, obviously this is the CFL. And there are two rules unique to Canadian football that allow this bizarre game of kickball to occur.
1) If you kick the ball out of the back of the end zone, you receive one point. It's called a single, or rouge.
2) You are allowed to advance the ball by drop-kicking it.
When Montreal lines up for what looks to be a field goal with time running out in a tie game, they're not even necessarily trying to split the uprights. If they can get it out of the end zone (rule 1), they get a point and win the game. That's why Toronto sends a couple of defenders back.
Since the end zone is 20 yards, and the goalposts are on the goal line, this 36-yard field goal is actually 56 yards to score a single (rule 1). The kicker doesn't have the aim for the 3 points, or the distance for the 1. The Toronto defender keeps it in play, but must get it out of the end zone, because if he's tackled there, it's still a rouge. But he sees he doesn't have the room to run.
He kicks the ball out of his own end zone (rule 2) to avoid being tackled and losing the game. But as luck would have it, it goes directly to the Montreal placekicker. Clearly he cannot run the ball in for a touchdown. But the opportunity to score the single is still in play. He kicks it back to toward the end zone (rule 2), trying to send it out the back (rule 1).
He again fails. But the Toronto player cannot control the ball and whiffs on his attempt to clear it out of the end zone (rule 2). There is a scramble, a Montreal player falls on it, and it's a touchdown. Montreal wins.
Got all that? Don't worry. All you need to know is that Canadian Football is Calvinball all grown up.
UPDATE: We've learned that Montreal was -4.5 in this one. So, you know, nice cover. (h/t Jason)