Canned meat. Open 'er up and see if it's still fresh.
In Quake, a Knight is an armored Monster that wields a sword. It only has melee attacks, but it is quick and can easily catch you if you're not careful. The Knight is only found in levels which are predominantly Medieval themed.
Knights are easy to kill; however, it is best to do so quickly, as their attacks are swift. Take out either your Super Shotgun or Nailgun, circle-strafe, and fire away. Use the same strategy when dealing with multiple Knights. From a safe distance, use the Grenade or Rocket Launcher; these weapons are generally one-hit kills as far as Knights are concerned.
With other Monsters, the Knight should be one of the first to go. The reason for this is because he rushes towards you at such a high speed, and while his attack power is meager at best, he makes up for it with the rate at which he swings his sword. Knights will generally go down in one or two shots, and the minor nuisance they bring is better dealt with as quickly as possible.
Because the Knight only has a melee attack, it is exceedingly rare for him to provoke a monster in-fight. It is, however, useful to have other monsters with ranged attacks (such as the Scrag or the Death Knight) hit a Knight; any creature at maximum health can take one down without much hassle, but not before receiving some damage themselves.
The Knight can still injure a player, even if both are on opposite sides of a wall. Oftentimes, the Knight can be tempted to continue swiping after the player has hidden behind the wall, resulting in the player taking damage even though an obstacle exists between him and the Monster.
To conserve Ammo, the player can attempt to use the Axe against this Monster by weaving between his attacks. Note that a similar tactic can be used on the Death Knight, though it requires a greater amount of skill than that needed to fight a standard Knight.