If you are sufficiently skilled in martial arts and you jump into a monster, you shouldn’t simply stop moving; you instead perform a flying kick that does extra damage or knockback.

Spell of control winds, a matter or evocation spell that fires a beam of wind that pushes monsters and objects away from the caster.

Shimmering dragons’ breath attack should be a “tractor beam” sort of thing, which pulls you towards the dragon most of the time, but occasionally pushes you back. This can pull or push you over dangerous terrain.

Add a “classical mechanic” monster as a counterpart to the quantum mechanic. It has a unique attack strategy; if it’s not in melee, it will rush towards you all at once and send you flying when it collides. This is an elastic collision that conserves momentum, so how far you are sent flying depends on how far it traveled to reach you and your relative masses.

If it is in melee range, it has a melee attack that drains your magic energy to make itself stronger, but if you subsequently kill it and eat its corpse, you regain exactly as much energy as you lost (conservation of energy). They also mutually grudge quantum mechanics.

When you deal a spinning back kick with martial arts, it should have an increased chance of knocking back the opponent.

A new spell called “forceful palms” that grants you a temporary buff. This buff increases the damage of your unarmed attacks, and either increases the chances of or guarantees the monster you hit will be knocked back.

Gas spore explosions should knock back any creature caught in them.

You can’t be knocked back if you’re carrying a loadstone.

If cast at Skilled or above, the spell of force bolt knocks back the first monster it hits (probably only 1 square like a monk’s staggering blow, or perhaps an Expert cast could provide additional knockback).

Wands of striking would not change since the Basic effects of the spell do not change.

Note that only two roles can cast force bolt at these levels: Knights (at Skilled) and Wizards (at Expert).

A #shove command, which allows you to shove a monster back one space, and will not anger most peacefuls, for the purpose of pushing peaceful monsters out of an altar room when they start crowding the altar you are trying to sacrifice things on. (Presumably, shoving a shopkeeper or priest or anything trying to stick to a specific location would not work the same.)

Artifact club The Pool Cue: it has the same damage as a regular club but causes several tiles of knockback to anything it hits.

Gnome punting: all kicks delivered to gnomes send them flying a few squares. (This also applies if a monster kicks the hero and the hero is a gnome.)

Ogresmasher can knock back (possibly entire groups of) small monsters it hits.

When a giant deals you a crushing blow and knocks you back, it can propel you into water you are flying or levitating over, wetting your inventory.

The player (and probably all creatures Large size or smaller) gets knocked back 1 tile when hit by a boulder (thrown or rolling).

Snow golem, which is a bright cyan ’ monster found in icy locales. Does not generate in Gehennom. It uses a spitting attack to launch snowballs (flavored as throwing them), which are an object which behaves like spat venom in that they disappear one way or another at the end of their flight. These deal damage and possibly knockback. The encyclopedia entry for snow golems uses “Frosty the Snowman” as reference material.

If you are knocked back when levitating, you should fly about 3 times as far, since you’re only being slowed by air resistance and not by e.g. your feet on the ground. This maybe shouldn’t apply to when you throw items when levitating.

The player can shove things, dealing no damage but pushing the monster back. The monster can resist and fail to be shoved; it will resist a lot if the terrain you’re trying to shove it onto is bad for it (like water). You can only shove if you have hands, and you cannot do it to small or tiny monsters. Possibly an AT_SHOV attack should also be introduced for monsters to shove the player.

If you deliver a staggering blow or other knockback to a cockatrice, and there is a monster behind it, that monster might get stoned.

Spell of shove: level 4 or 5 escape spell. At Unskilled and Basic, it fires a beam that pushes the first monster it hits back one space (as if receiving a staggering blow, but doing no damage); at Skilled and Expert, it fires a shorter-range beam in all eight directions. What with shoving monsters into moats to drown them and things like that, this could be a pretty fun spell.

If you are wearing iron shoes, you cannot be forcibly knocked back to other spaces, unless you are levitating.

Add a knockback attack and a monster that can use it. Getting knocked back into a wall deals some extra damage, and getting knocked back into water or lava has predictable effects.

Carried loadstones should prevent knockback, including Newton’s Third Law effects. Possibly they should prevent levitation entirely.

Wind dragons, a cyan D whose breath is a wind beam: it doesn’t damage you, but blows you backward, and can’t be reflected. Their scales grant flight, which should confer resistance against knockback and Newton’s Third Law.

Add a bull rush command that lets you shove a target monster back one or more squares. The relative size of the monster and hero and the strength of the hero are important factors. The hero might move into the space of the displaced target.