Chase Rules for D&D

A chase is not the same as tracking. A chase is an exciting or tense scene where a chasee is fleeing from an immediate chaser. Chases are important because they add variety to a game but they are also challenging because they require use of many DM skills rapidly.

Chases are similar enough to combat that many of the same rules apply such as initiative, turns and rounds, actions, and movement. The major difference with a chase is scale. While a combat may take place in a single room, a chase occurs on a chase route, path, or course. A long chase may cover many rooms and a variety of spaces on its course. The chase route can cover an entire town, forest, maze, or ancient labyrinth. Because of the scale of a chase, you're going to have to rely on theater of the mind and a lot of good narration so that the players know where they're at and what's around them.

Terminology: The pursuers chase their quarry. A quarry flees its pursuers.

Goal: How does the chase end? If pursuing a quarry, are you just following them to their secret lair or are you attempting to corner and capture them before they can hide or escape? If fleeing pursuers, are you searching for a place to hide, are you trying to outrun your pursuers and escape, or are you leading your pursuers into a trap? 

Chase Route: An NPC trying to escape the PCs may travel a fixed chase route the GM has determined in advanced with few improvised changes. If the PCs are fleeing an NPC, they may need the GM to tell them possible twists or turns they have available each round or for each new space they enter.

Time: A chase is measured in rounds, same as combat. Each participant in the chase gets one turn per round.

Initiative: The DM can decide that initiative goes to whoever initiated the chase. Otherwise, roll initiative the same as combat.

Running: During a chase, it is assumed that all participants will their move action and use their action to move again. Players may specify that they slow down or stop. During a chase, creatures move at their maximum move range each turn and have a -5 penalty to perception. Characters become exhausted after running for 30 turns in which case they take a -2 penalty  to attack and damage rolls, and to AC. Mapping is not possible during a chase.

ACTIONS
Creatures get actions in a chase just like in combat. Creatures must stop to use an action for something other than making a second move. It is recommended that chase participants use their action to move again. Pursuers who stop to use an action to attack or cast a spell risk losing their quarry; A quarry who stops to use actions risks being caught. This can be used to attack, cast a spell, draw and use or throw an item, or to deliberately avoid an obstacle. You can make a threat "you're only making things worse for yourself!". You can try persuasion "stop, let's talk!" You can declare that you'd like to search for something specific while moving that you can make use of "I break my sight with the quarry and look around for a horse I can mount." Chase participants can not ordinarily make attacks of opportunity.

Attacking While Moving
-It makes sense that creatures should be able to move and make an effective melee weapon attack, a shove, a grab, tackle, or trip an opponent in a chase without sacrificing a move action and losing significant distance, Imagine one American Football player sprinting and tackling another sprinting player or a slide tackle in soccer. As for baseball, I think I could chase someone with a stick while swing at their head without consistently losing 30 ft each attempt.
-Attacking while moving, also called a charge, should be a standard action in core rules if not a feature for martial classes. Charging trivializes the Charger feat.
-Charge: When you use your action to Dash, you can use a bonus action to make a melee weapon attack or to shove.
-Spells requiring a bonus action to cast can already be used by dashing wizards while dashing. Why not charge attacks?
-Optional Rule: Charging attacks may make use of the monster feature Charge where additional damage is applied to attacks based on differences in size classes.

OBSTACLE COURSE
    Because creatures generally move at the same speed, or some creatures may simply outpace others, participants in a chase will rely on fixed or moving obstacles to effect the distance between the quarry and the pursuers in their favor. Once a creature passes a fixed obstacle, that obstacle is out of play, like fence you vault over. Random obstacles may even join the chase like a city guard. Obstacles may be obvious or hidden, or somewhere in between. Obstacles may be small enough to only effect one creature such as a discarded banana peel or large enough that all participants have to avoid it, such as a gap between two roof tops.

    Some obstacles will halve a creatures move range for that turn. Some obstacles will stop a creature in place and even knock them prone. Anything that difficult terrain rules applies to may slow a creature such as  dense forest, but other examples include a crowded street. Obstacles that cam stop a creature are obstacles that can cause tripping and falling such a tough root sticking out of the ground hidden by tall grass or a pot hole.

    Obvious obstacles might be seen several turns in advanced allowing players to anticipate them and plan for them, like an oblivious merchant pushing  a cart of cabbages. Hidden obstacles might surprise a player and take them out by chance.

    DMs should have a table of obstacles you can roll on or at least reference. The table will be based on the setting. An urban setting for instance has thick crowds, playing kids, peoples pets, merchants with carts, trash, an elderly man with cane, workers on ladders, laundry lines, people carrying too much stuff that goes flying when they inevitably drop it, and the occasional beast of burden taking a dump.

In a dungeon, obstacles include monsters and traps which may present themselves at any time making a chase in a dungeon very risky.

Distractions: Some creatures may be distracted by thrown food or treasure allowing someone to escape.

Line of sight: Most monsters give up their pursuit if PCs are out of their range of vision. Darkness must be lit with a light source. Light sources allow normal vision up to 30 ft. Chase participants may make a lot of noise and can still follow or flee the sounds of their opponents who are hidden from view.

ENDING A CHASE

Hiding and Evading: A quarry with a substantial amount of distance on their pursuers can make a stealth check and hide in a room or in a fixed spot, such as behind some crates in an alley. The quarry may make a stealth roll to evade their pursuers and continue on their way without detection. Quarry may have advantage if their are a lot of places to hide or disadvantage if there are few places to hide. They may have advantage in crowded or noisy places and disadvantage in open, quiet places. If the lead pursuer is skilled in tracking, the quarry may have disadvantage on a stealth roll. 

Capture: Pursuers may close the distance between themselves and the quarry and attack or tackle and pin the quarry. The pursuers may simply corner their quarry in a dead end or at the edge of a cliff.

Exhaustion: Creatures who are too exhausted to continue the chase drop out or are caught.

BEFORE A CHASE
-Determine the who is the quarry and who is the pursuer
-Distance: DM determines distance between quarry and pursuers. Sides of a conflict can spot each other from 2d6 * 10 ft away.
-DM determine Surprise; Surprised creatures may not notice their opponents until 1d4 * 10 yards away.
-DM determines initiative and/or calls for initiative rolls

SEQUENCE OF A CHASE:
Step 1. Descriptions. The DM determines and describes features and obstacles that appear of the chase route this round.
Step 2. Actions. The players decide their actions. The DM decide the NPC actions.
Step 3. Descriptions. The DM determines and describes the results of player actions.
Step 4. Descriptions. The DM determines and describes the results of NPC actions.
Step 5. End turn. The PCs record resources spent. The DM records what round of the chase has passed and what features or obstacles are passed. The DM determines what distance was lost or gained. The DM determines who is the current  lead pursuer.

How to Run Your Chase
Players should have a sense of what features are on the chase route such as scenery or buildings. They should know what feature they are passing, what feature is right in front of them, what feature is coming up in the next few turns, and what features are just appearing in the distance. Your entire chase route could be simplified as a list of features with their distances in between and the distances would be represented as number of turns apart. You wouldn't number the features 1, 2, 3, 4, etc., instead you would number each feature 1, 3, 5, 8, based on the round when the players will encounter that feature. Cross features off the list as they are passed. Provide brief and simple narration at the start of each round. For example, "You pass feature A, a short distance away, you see feature B, and further away still is feature C. The quarry keeps running. 'You morons are persistent!' he yells. Bob, what do you do?" Shorter narration emphasizes the pace of a chase scene.