Weapon heckling is a tactic where a agile class forces their opponent to switch weapons rapidly based on the distance between the two players. Weapon heckling is useful when performed as a scout due to your speedy movement speed, but learning about weapon heckling and countering your natural reaction to switch weapons can help you defeat a scout. A pronounced example of weapon heckling would be scout vs pyro – the flamethrower is only useful at close range, a scout would get in close while strafing to get high damage shots in, and then retreat while the pyro is switching to his flamethrower. The same thing can be performed across other classes and give you a boost in one vs one combat.
The Concept
Exploit the classes weaknesses in range and force them to switch weapons in order to be effective. Move in when they switched to a medium range weapon, move out when they switched to a close range weapon, so they will not be able to use their weapons to the maximum effectiveness. Pistols, which are better at medium range are a recommended weapon if you want to use this to the full potential.
It takes 0.8 seconds normally to switch weapons. Watch their arms to know when they are switching, and the animation tells you what weapon they are switching to. You must me moving unpredictably and surprisingly to make it harder for them to hit you, and direct their attention to that instead of what you’re pulling off.
Class based specifics
Good to heckle:
Pyro: The pyro is the easiest class to exploit because of the limited range of the flamethrower. The problem is, if you get ignited the afterburn will take away a huge chunk of your health. Keep in mind the flamethrower range varies based on the direction of where the pyro is moving – backpeddling gives a longer effective range. When you’re outside their primary range, attack them and force the pyro to switch to their secondary, then get close and meatshot him. Repeat as needed.
Heavies are massively powerful with their minigun at point blank range, and it’s still effective at medium range too. Make sure to surprise the heavy with some unexpected meatshots (when he’s not spun up), and retreat behind cover. After you stop hearing the spun up sound and he starts to go for the medkit or eat his sandvich, come back and finish him off. Alternately, if a heavy is already weakened spin in circles and jump around him.
Medics: They’re easy to heckle. The primary syringe gun is good in close range but pretty much useless in close / point blank, so move in close while they’re using their primary and when they switch to their melee, move back out again. If the medic is pocketing someone, make sure to get rid of the medic first and retreat if the patient has noticed, as the element of surprise is crucial.
Soldiers are a bit more challenging but you should be able do dodge all their rockets at medium range, especially with double jump if you need it. When the soldier switches to their shotgun (if they have it equipped), get in close and end it with a killing meatshot.
Classes that you should be able to easily kill regardless: Snipers, Spies, Engineers.
Countering weapon heckling:
It’s possible to counter against scouts using this technique. First of all, you can fakeswitch. Switch to another weapon, but instantly switch back and catch the scout offguard. Secondly, stick to one weapon and if you have no others that are okay across all ranges, use the terrain to your advantage and force the scout to come close.

I’d just like to point out that this tactic is significantly reduced in effectiveness against Pyros with the Degreaser – near instantaneous weapon switch renders heckling pretty much redundant.