This is a page listing exploits the player can use in Team Fortress Classic, including instructions on how to use each one.
Teleporting the Flag
When a player throws a flag, there is a cooldown before they can pick it up again. When a player 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 one second before the player is moved. A method to teleport the flag can be performed 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, thus you will then automatically pick up the flag and arrive at the exit with the flag in hand. This 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.
Shooting Crowbar / Alternative Weapon Fire
Players are able to use a different weapon to fire another weapon's attack. For example, a Crowbar shooting rockets is possible for a Soldier, or a Spy Knife shooting Super Shotgun Rounds.
Swap to your "Off-weapon", such as a crowbar, then back to the "Main Weapon" you wish to fire such as a Rocket Launcher. Hold fire until all of your ammo has been spent for your Main Weapon, then while still holding fire, press your "Use last weapon" bind twice, then collect some ammo. This will then allow you to shoot ammo from your main weapon while displaying your off weapon, even to other players on the server.
This resets when the player changes weapon or is killed.
Well Out of Bounds
When playing as Demoman, head for the water area from spawn and drop down the hole. Follow the pipe until you get to a square section right outside the tunnel. Set a Detpacks in the center of the square, move to the corner opposite the tunnel, face the Detpack, and push into the corner. If done right, you should be out of bounds.
This next one is best done as Soldier. From the tunnel where you exit, hop out of the square area and there should be a part sticking out from the nearby wall. Jump onto it, get onto the dead center, and crouch while walking forward. Yet again, you should be out of bounds.