|Damage vs. small||1d6|
|Damage vs. large||1d8|
|Base price||10 zm|
A lance is a weapon in NetHack. It is meant to be used while mounted and gives a chance dependent on your lance skill of jousting a monster on a successful attack, granting additional damage, stunning the victim, and often causing it to be pushed back a square if it is not already dead. This will sometimes cause your lance to break.
A lance can also be applied to attack two squares away (a knight's jump away or even diagonally if sufficiently skilled). However, there is a to-hit penalty for applying the lance when the wielder is at basic skill level or lower. It is possible to stay a knight's jump away from monsters who are able to throw missiles and use spells and breath attacks to attack them with the lance without them being able to retaliate.
When attacking an adjacent monster in melee with a lance while mounted, there is a chance that you will joust the monster. 
- You deal an additional 2d10 damage (2d2 if the lance is your secondary weapon). In SporkHack, 2d10 is replaced with 2d(5 + level / 3).
- The monster loses all its movement points, and is thus unable to act (again) this turn.
- The monster is stunned. This has little effect except making it easier to hit.
- The monster is pushed back one space, unless it is too heavy (huge or larger), that space is occupied or deadly (e.g. a lava pool), or it cannot move (e.g. it is trapped).
- Your lance has a chance of breaking. Positive luck will greatly reduce this chance. Your lance cannot break when jousting an unsolid monster. Artifact lances will never break (they also don't exist). Enchantment and beatitude do not affect the chance of the lance breaking. 
The approximate chance of your lance breaking per attempt to hit a solid monster is provided here:
Luck Break Chance -13 1 in 18 -5 1 in 43 -1 1 in 126 0 1 in 250 +1 1 in 9550 +5 1 in 10500 +13 1 in 12500
Your chance of jousting is determined solely based on your lance skill (or, if you are using two weapons, the worse of lance or twoweapon):
Rank Jousting Chance Unskilled 20% Basic 40% Skilled 60% Expert 80%
The lance is an extremely heavy weapon (more so than any other weapon in the game except the heavy iron ball), and its base damage is quite low. If you simply want a weapon for pounding, any other polearm is preferable to it. However, jousting more than makes up for the lance's base damage and allows it to become potentially the most powerful non-artifact weapon in the game, making it well worth using.
Jousting can cause your lance to break; as lances are difficult to come by, it will be hard for you to find a replacement should yours break. Positive luck reduces the chance of breakage. With luck less than or equal to zero, you should probably only apply your lance at range, and switch to another weapon or fall back when opponents close.
A deadly jousting tactic is to let the monster close to applying range, then apply the lance on it until it moves adjacent, then hit it normally. Since at high skill levels a joust is nearly guaranteed, the monster will be pushed back for another round of lance thrusts, then will move adjacent again only to be jousted and so on until the monster is dead, usually without ever having an opportunity to attack.
With their jumping ability, even low skill Knights in an open space can make particularly good use of the strategy of keeping just enough distance between themselves and an opponent to apply their lance, denying it an opportunity to retaliate.
Because jousting robs monsters of their movement points, at high lance skill many single opponents can be readily dealt with simply by repeatedly attacking them in melee with a lance. A successful joust will guarantee you get another turn before they can act. If you are fortunate enough to get jousts on the first action of every game turn, this will immobilize even extremely fast monsters. If the opponent in question is slower than normal speed, such as many of the Named Demons, they are unlikely to get a single turn before you are through with them.
How skill affects range when applying a lance:
The @ is where your character is standing. Spaces marked with a x are too close to be hit, spaces marked with a U can be hit even while unskilled, spaces marked with a S can only be hit when skilled or expert, and spaces marked with an E can only be hit when expert.
The lance is the only weapon to use the lance skill, and there are no artifact lances.
A lance is basically a type of spear designed for jousting from mounted warriors. The stereotypical European knight's lance has a vamplate, to prevent the hand from sliding upon impact. They were usually one use only and often broke.
With this the wind increased, and the mill sails began to turn
about; which Don Quixote espying, said, 'Although thou movest
more arms than the giant Briareus thou shalt stoop to me.'
And, after saying this, and commending himself most devoutly
to his Lady Dulcinea, desiring her to succor him in that trance,
covering himself well with his buckler, and setting his lance
on his rest, he spurred on Rozinante, and encountered with the
first mill that was before him, and, striking his lance into
the sail, the wind swung it about with such fury, that it broke
his lance into shivers, carrying him and his horse after it,
and finally tumbled him a good way off from it on the field in
Cervantes Saavedra ]
- joust.c in src/uhitm.c in NetHack 3.6.0
- Breaking: 1/5 of the time, if rnl(50)==(50-1), the lance will break. It has a chance of 0.4% at 0 luck, about 0.01% at any positive luck, and for each negative luck the chance increases by about 0.4%. See Source:NetHack 3.6.0/src/uhitm.c#line1256
- src/makemon.c in NetHack 3.6.0, line 196
- src/objects.c in NetHack 3.6.0, line 236
- src/u_init.c in NetHack 3.6.0, line 74
- src/apply.c in NetHack 3.6.0, line 2879