Team Fortress 2/Scout

The Scout is the fastest and most agile class in Team Fortress 2. They have 125 points of health. They can double-jump, unlike any other class, and capture any control point twice as fast. They carry:
 * a scattergun (weapon 1) - this is like a sawn-off double-barrelled shotgun with a lever-action reload mechanism. Because it spreads out significantly this weapon's use diminishes quickly the further away you get. It also takes some skill to aim it whilst moving at speed, but this weapon is lethal at close range, especially if you can get behind an enemy without them knowing. Two or three shots at point blank will kill most things.
 * a pistol (weapon 2) - this is the scout's main long-range weapon, since the scattergun is little use at any great distance. It doesn't inflict much damage per shot but 5 or 6 will kill another Scout and in some ways it can be easier to aim than the scattergun.
 * a baseball bat, with team logo (weapon 3) - this is the Scout's melee weapon. All melee weapons in Team Fortress 2 are quite powerful, being able to kill weaker classes like Medics in three or four hits, but the Scout's bat swings a little bit faster than other melee weapons of other classes.

Using the Scout
The Scout's speed is their main advantage, so especially with capturing missions they can reach the control point fastest. It obviously slows down enemy capturing if you've already begun to capture a point, which is a lot quicker as a Scout. Scout rushes work extremely well attacking-wise providing you are not playing a map like Gravel Pit or Dustbowl where the enemy has time to fortify a point before you attack. Sometimes however, multiple Scouts can easily overwhelm defences and defending players of pretty much any class (except possibly the Pyro) - the more Scouts in a rush, the better.

Learning to aim at speed as well as controlling the Scout's airborne movement is also important, so that you can land point-blank blasts with your scattergun without being in enemy fire for too long. Jumping over the heads of players is a good tactic, but most of the time you can outrun any pursuers and circle around them. The Scout double-jump ability also allows them to exploit paths that are unavailable to any other class, such as running across roofs or the tops of large objects, putting them largely out of harm's way.

The Scout's low health means that they can't take much punishment before they die, and because of their speed quickly become targets for anybody nearby, and even their speed can't outrun some enemy fire. In particular one Pyro ambush with a flamethrower spells almost certain doom for a Scout unless they are very close to a health pack or water. It's a good idea to stick behind cover as much as possible as a Scout, unlike the Heavy, for example, who has enough health to take a battering out in the open.

Defeating Scouts
Scouts have low health, so good aim with any high-damage weapon such as a Soldier's rocket launcher or the Heavy's minigun will quickly dispose of a Scout, as will about a second or two of exposure to the Pyro's flamethrower. Ambushes are often the only way that you can land a hit on a Scout with the short-range flamethrower, but even a small lick of fire will continue to eat away at the Scout, often leaving them with little health, or even killing them. The Scout's scattergun has a slightly greater potentially-lethal range than that of the flamethrower, but the Pyro has more health.

Sentries are also effective against Scouts, since they have excellent aim, and can kill a Scout on full health in next to no time, especially upgraded ones. Failing that, use another Scout; if they have good aim and can surprise them, they can deal a lot of damage and leave the weakened Scout for disposal by someone else.

So, a Pyro and a sentry are probably the most effective ways of dealing with Scouts. Be warned, however, that a Scout can be deadly indeed, and can inflict a lot of damage in little time, especially if they surprise you (or there are more than one).