How do I adjudicate a player trying to sweep kick an enemy's legs to knock them down?

Question

I'm new to D&D. I already read both the Player's Handbook and Dungeon Master's Guide (I'm mastering) and I would like to know how I could handle this situation:

A player wants to do a sweep kick on an enemy's legs and knock him down. He rolls a 20 and does the damage, but what about taking the enemy down? There is no rule that covers it.

Following the rules, the player would have to do a specific action to try to push the enemy down, and there would have to be a resisted check to see if the player can actually drop the enemy, so how could I deal with that?

Answer 1

There are rules for this.

Shoving a Creature in the PHB allows you to use an opposed strength check to push a creature 5ft away or knock them prone. This is done instead of an attack (you don't get to deal damage)

Trip Attack is a manoeuvre available to the Battle Master subclass of the Fighter. On a successful attack you can spend a superiority die to make an opposed strength check to knock the creature prone (similar to above, but this time you get to deal damage as part of the feature).

Shield Master is a feat that allows you to make a shove (as above) as a bonus action using your shield if you have taken the attack action.

As you can see, there are many options that can do what you want.

You will find that many 'real life things' in D&D are balanced against 'What is fun'. What works for your PCs also works for the monsters. And when a group of bandits ambush your friends and simply cut their legs off from behind (because it's what could happen in real life), the game quickly becomes less fun.

Answer 2

This particular case: be a Battlemaster

To simultaneously hit an enemy and knock them prone, you can use the Fighter's archetype Battlemaster, who has access to combat maneuvers. One of them is Trip Attack, on Player's Handbook page 74. It allows attempting to knock a target prone while dealing damage.

More generally, you shouldn't

Dungeons and Dragons is not a realistic game nor is it intended to be. For the sake of simplicity and balance, the combat system doesn't cover every possible fancy maneuver there is. You can of course houserule different actions in as fast as your players can propose them, but I'd argue most additions introduce more complexity than they're worth. Gauging the balance and ramifications of house rules is hard, even for more experienced GMs, so I wouldn't get started on overhauling the entire combat system just for the sake of introducing realism.

Another concern is accidentally changing the balance between classes. For instance, suppose one of your players was a Battlemaster and had the Trip Attack maneuver. By houseruling that every character can do it, you effectively robbed the Battlemaster of one cool special feature: similar to how the Wizard would lose uniqueness if suddenly everyone could cast fireballs.

Answer 3

Just to address your final point, any martial artist can tell you that it's remarkably easy to kick someone in the leg and only succeed in bruising their leg, not taking them down. A pure sweep (without the pushing element from a grappling art) requires you to hit their foot or ankle (not just lower leg) with a kick which at the point of contact lifts their foot. The classic mistake is simply to kick through, at which point either you bounce off or they just stumble.

My point is that in RL this does need a skilled person to nail the technique. It's not something that your average person can do - hence the special ability already mentioned.

Your average person can grapple and stick a leg out though - so the answers about grappling are valid for that.

Answer 4

Without violating the action economy? Play a Monk; Way of the Open Hand

TLDR: by using the Furry of Blows, a Way of the Open Hand Monk can do things like hit and knock down an opponent in combat that you want to do; the sweep kick gets translated mechanically as "try to knock an opponent Prone." (Details below in Monk section) With that said ...

How D&D 5e is set up to work

D&D 5e is a turn-based game that vaguely emulates actual combat when combat happens. What it is trying to capture in the six-second combat round is all of the fast and furious action that both sides in the battle are taking. (See more below). It thus has an action economy that will or won't enable some cool stuff to happen within the constraints of the turn-based combat resolution method. Remember: the whole time your character is trying to do cool and deadly stuff to the enemy, they are trying to do the same to your PC. Who gets to go first is deliberately randomized via the initiative mechanic at the start of combat.

What's this action economy thing?

Action; Bonus Action; Reaction; Movement; Interact with an Object. (See Chapter 9, Combat, for details). You get to do one of each, although a bonus action and a reaction are usually conditional on some other game feature. (And there are many. The link has an answer to one such case where I laid out the action economy).

If you, the DM, can fit what your players are trying to do into that action framework, so much the better.

1. Some of the unusual or cool actions during combat can be improvised, but there is an action cost to doing this. (Chapter 7, Using Ability Scores).

   Improvising an Action (Basic Rules, p. 72; PHB Ch 9)
   Your character can do things not covered by the actions in this chapter, such as breaking down doors, intimidating enemies, sensing weaknesses in magical defenses, or calling for a parley with a foe. The only limits to the actions you can attempt are your imagination and your character’s ability scores. See the descriptions of the ability scores in Chapter 7 for inspiration as you improvise. When you describe an action not detailed elsewhere in the rules, the DM tells you whether that action is possible and what kind of roll you need to make, if any, to determine success or failure.

   A PC can choose to use their action to, rather than attack, do something Athletic (or even Acrobatic). This is typically resolved by using the ability check mechanic: Strength (Athletics). The DM sets a DC for whatever cool thing the character is trying to do, and a d20 roll resolves it. The sky is the limit.

   • Swing from that chandelier!
   • Knock that table over!
   • Dump the boiling water in the cauldron on your enemies!
     
     The DM's task is to figure out how difficult this is (set a DC for the attempt) and whether or not an opposed check/contest is the suitable thing to do. (See Contests in Chapter 7).
     
     
2. Something to remember as the DM: a variety of gamisms are built into the game such that resource management is a factor. Some examples of this are:
   • limited spells slots
   • limited class abilities that reset on a short rest
   • limited "powers" that represent that only now and again is there an opportunity to have that cinematic / cool thing happen
     • Barbarians Rage is not unlimited; the Fighter's Action Surge is a limited resource as well; other examples abound.
       
       All of the above is put into combat resolution in an attempt at game balance.
3. Called Shots: Your "shooting someone in the hand" is not "real life" stuff; it's Hollywood / TV / comic book / fictional cinematic cool stuff. Makes for a good scene, and a good story, sure. (In my formal firearms training, I was always taught to aim for center of mass). Called shots do not have a mechanic in this edition of the game but there are some good suggestions on how to work with that idea in this answer. _{This element got edited out of the question, but I'll leave it here anyway}

Why do I suggest Monk?

Caveat: there is usually a cost for doing cool things, such as giving up an attack (as noted above) or in the Monk's case a ki point cost. (Ki points reset on a short or long rest).

When you spend a ki point to set off a Flurry of Blows ...

Immediately after you take the Attack action on your turn, you can spend 1 ki point to make two unarmed strikes as a bonus action.

... the Open Hand Technique at level 3 provides these cool options during combat:

• Knock an enemy prone if they fail a Dexterity check
• Get pushed away {or off of a cliff} by failing a Strength saving throw
• Can't take reactions until the end of your next turn {that opponent will have no chance to make an opportunity attacks against you or your allies since an opportunity attack requires a reaction; see action economy above}

Notice that there is a chance for failure in two of the three above cases. The PC tries to do a cool thing, but since the enemy isn't just sanding there it may or may not work. There isn't a video game style "I win" button; there is a chance of failure because the enemy is trying to do you in while you are trying to do in your enemy.

This is combat

Have you ever been in a fight? Boxing? Wrestling? Martial arts? You are working in a dynamic, interactive environment. Unlike Hollywood's "set up" combat scenes, your opponent isn't just standing there waiting for you to get all awesome on them. They are making it difficult for you to achieve your objective during the six second combat round. What's going on in the round is happening more or less at the same time, except that the initiative order makes it easier in the game to take turns in an orderly fashion so that play moves along. D&D is a turn based game that vaguely emulates actual combat: it is not a reality simulator.

More cool combat things done by Monks

Besides using a weapon or unarmed strikes, Monks can:

• Stun their opponent at level 5.

• Catch a missile and throw it back at the enemy with the Deflect Missiles skill at level 3.

  There are die rolls involved; there is no automatic "I win" button.

In summary ...

As an answer to your question that is different than the other answers: to do more cool things in combat, play a Monk using the Way of the Open Hand tradition.

Answer 5

Other answers cover the specific case of knocking down an opponent.

For more general scenarios, where a player character (or monster) wants to do something not covered by existing rules, you as DM will have to make a ruling on how to represent that action within the game.

Some guidelines on this, which I personally try to follow when adjudicating player and monster actions in combat:

• Whenever possible, compare with existing rules that do something similar. Get familiar with the "Actions in Combat" chapter of your PHB, in particular Contests and the Help Action, which are very useful as general guidelines.
• A "rule-of-thumb" is: Your ruling should be of similar power and cost as other options available for all creatures and significantly weaker (or having a significantly higher cost) than class or racial features. An exception can be made where extraordinary environmental conditions allow something special that wouldn't normally be possible.
• If a creature wants to do something directly opposed by another creature, the game already provides a framework in the form of a Contest (described in the aforementioned actions in combat). Alternatively, you may choose one of the following options:
  1. If it is something, against which armor or dodging could help, model it as a special Attack (which usually won't do damage - there are already rules for that)
  2. For something a character wants to do that does not directly affect another opposed creature, ask for an Ability Check (decide on an appropriate ability, DC and whether proficiency applies), see the chapter Improvising an Action.
  3. For something a character wants to avoid happening to them, ask for a Saving Throw (of an appropriate DC).
• Most things, especially any action directly affecting another creature (enemy or ally), will probably cost at least an Action to perform. Particularly small actions might be modeled as Bonus Actions or even Object Interactions, but this should be the exception, not the rule. To have someone react to something outside their own turn, you can use a Reaction, although this should be used very sparingly and for minor things, since it otherwise risks being more powerful than the Ready action.

An example to illustrate things: Your player characters are fighting a pirate captain aboard her ship. One player announces that his character will try to entangle the captain in the ropework hanging around.

First we decide on the execution: This is a nontrivial thing, requiring both time and concentration, so we will model it as an Action the character performs. Dodging or a shield can help the captain avoid the effects, so we decide to require a successful Attack by the player. Unless they can demonstrate a special skill they have with ropes, it is an improvised attack without proficiency. (Note: we could also have modeled it as a Contest instead, using Dexterity vs either Dexterity or Strength.)

Being entangled in ropes usually imposes the "restrained" condition, so we could decide to replicate that here. This is a more powerful effect than other actions (like Shove or Help) can provide, but we can excuse that with extraordinary circumstances (lots of ropes hanging around) - in other circumstances, we would only allow the player to momentarily disorient the captain or snag an arm or a leg for a few seconds, which would be modeled by the player using the Help action.

So you say to the player: "Sure, you can do that. You will have to take your action to try, and hit the captain with an attack, using the ropes as an improvised weapon. If you succeed, they will be restrained until they can manage to free themselves."

Answer 6

I understand your problem. You always read that you can do everything you want in combat, that a fighter doesn't just have to say "I attack" every round. But it's hard to make creative play worthwhile while not unbalancing the game. Basically everything the player could consistently repeat is not something you can rule favourably.

In your case your player wants to do something that takes 2 actions in one action. You can allow it, but you have to make the success chance lower than half for both actions. So more than half his chance to hit, and more than half his chance to succeed on the Strength contest. A simple method to do this would be to let him roll normally, then roll an extra 2d6 for each action. If it's lower than 8 he fails the part of the action.

If he wants to get advantage for attacking a knocked-down enemy, the chance to succeed should be even lower.

If the player wants an advantage, he has to use something unique about the situation.

Now as for the realism and called shots (I want to shoot him in the hand so he drops his sword): You can easily do this, BUT only if it is the finishing attack. So if it would make the enemy no longer a threat you can only do it when it reduces him to 0 health. Then a normal attack can become "With a flurry of attacks you decapitate the bandit" or "you aim for his hand, hit it with a satisfying thunk and he is out of the fight".

The HP system is an abstraction of when an enemy is unable to fight any longer. It can even be "you finally manage to twirl his sword from his hand, with a swift step you are on him, threatening his throat with your dagger". In this case, the enemy could have no physical injury at all. The damage you dealt to him weakened his defense and brought you into a better position to execute the final attack (note, you need to describe it like that all fight long).

Let's say your player wants to shoot the enemy in the legs to take him out of the fight. So, his first attack "hits". You Mark down the damage it would do, then say "Your arrow goes straight for his legs, but he dodges with a rapid motion, losing his balance. You got closer to your goal, but it will take more arrows to take him out.". The next arrow that hits may be described as "you aim for his legs, but he deflects with his left arm protector while his face distorts in pain".

Answer 7

I know its an old thread, but for other people who might look for it. On page 195 of the Player's Handbook

Contests in Combat (PhB p.195)
Battle often involves pitting your prowess against that of your foe. Such a challenge is represented by a contest. This section includes the most common contests that require an action in combat: grappling and shoving a creature. The DM can use these contests as models for improvising others.

You could call for a Strength (Athletics) or Dexterity (Acrobatics) opposed check to trip an opponent. This of course should not be cause damage, as shoving and grappling a creature don't either.

Answer 8

In the RAW there is only the above answers to efficiently knock down an opponent.

This is also dnd, meaning that anything you can imagine you can feasibly do. The only thing stopping someone is dice and The DM (which you said you are).

In our game, we are granted the ability to do whatever we want as long as the dice say its ok.

How we would go about knocking down an opponent would be: Roll str to grapple leg versus opponent roll. Roll str vs opponent to pull his leg out from underneath him. Roll dex (acrobatics DC-12) to move out of the way to avoid being hurt in the process.

This would be a full turn without movement. This may not work for everyone, but at the same time its a way to do something like this without a special ability and also a way to do it without "breaking the game" Because there is a high chance it would fail.