A Symmetra player accidentally baited her team by falling off the map. As the match begins on offense for the blue team, Symmetra immediately heads over to the ledge to try to pull off the teleporter flank. By moving ever so slightly to the left, you can see the other side, and you can plant the teleporter.
If you work fast enough, the whole team skip past the choke point. Or like in this clip, you can watch the Symmetra fall to her death. Even if you do land the teleporter spot, it can still be dangerous, if the team is aware of the move, it's fairly easy for an enemy Lucio to boop a few of your allies off the map.
Only try this if you are committed and fast, and if you haven't tried it before. Or if you can fly or have movement abilities like Wrecking Ball, you can get to the ledge by yourself without a teleporter. This works great if you team will stay toward the choke point distracting them, and as soon as they turn around to deal with the flanker, you rush.