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Teleporting the Flag
When a player throws a flag, there is a cooldown before they can pick it up again. When a play stops over a teleport entrance, the game checks to see if they have a flag on them. If they do, the teleportation is canceled. The actual process of teleporting takes about a second before the player is moved. A way to teleport the flag can be seen by creatively combining this information.
Begin by picking up the flag and throwing it on to the teleport entrance. Wait about 5 seconds then move onto the teleporter. If timed correctly, you will not pick up the flag and will start to teleport. The cooldown for picking up the flag will then expire mid-teleport. You will then automatically pick up the flag and arrive at the exit with the flag in hand. This amusing glitch is not feasible in a normal game due to the difficulty of getting an Engineer into the enemy's flag room and keeping the setup alive.