Guide

Game ground bounce systems explained

Harbor Brawl's aerial routes dead-ended the moment a juggle touched the floor. Launcher enders that should have popped opponents back into the air instead triggered a flat knockdown with no follow-up — players called them “combo taxes.” Worse, two unrelated moves both applied a visual floor skid but only one actually opened a relaunch window, so training-mode frame data lied. After introducing explicit ground bounce tiers, a per-combo bounce budget, and a shared floor-pop FSM tied to juggle decay, legitimate floor-to-air conversion in ranked duels rose from 12% to 38% and average combo route diversity (unique ender paths per character) doubled in a 9,400-match soak.

A ground bounce pops a falling or downed defender off the floor into a brief airborne state so the attacker can continue a juggle, bridge into OTG pressure, or reposition before wake-up. It is distinct from wall bounce (horizontal geometry reflection) and from hitting someone while they lie prone — ground bounce changes vertical state. This guide covers bounce taxonomy, height and timing math, juggle and OTG integration, knockdown interaction, the Harbor Brawl refactor, a technique decision table versus hard-knockdown-only enders, pitfalls, and a production checklist.

What ground bounce is

Ground bounce occurs when a defender's body intersects the floor collision plane during juggle or certain knockdown states and the engine applies an upward impulse instead of entering full grounded knockdown. The defender becomes briefly airborne again — usually with reduced hitstun and a visible “pop” animation — allowing one or more follow-up hits before untechable fall or hard knockdown.

Ground bounce solves three design problems:

Combo extension past juggle floor — reward labbed routes that do not require infinite wall carry.
Ender differentiation — same launcher family can end in hard knockdown (neutral reset) or ground bounce (conversion) with clear tradeoffs.
OTG bridge — some games allow a single OTG hit after bounce before relaunch, linking floor systems without full prone oki.

Term	Meaning
Floor pop	Small vertical impulse; defender rises ~1–2 character heights
Slam bounce	Heavy ender drives body into floor, high pop with long hitstun bonus
Bounce budget	Per-combo cap on ground (and often wall) bounces before forced HKD
Relaunch window	Frames after pop where aerial moves reconnect at reduced scaling
OTG bridge	Optional grounded hit allowed between pop and relaunch (once per bounce)
Flat landing	No bounce — immediate soft or hard knockdown, oki begins

Ground bounce taxonomy

Tier 1: Passive floor pop

Any juggle that reaches the floor while budget remains triggers a small automatic pop. Common in anime fighters and brawlers. Tuning levers: pop height (pixels or % body height), hitstun on landing from pop, and whether gravity scaling resets. Risk: passive pops homogenize enders — players stop choosing knockdown enders because the floor always gives another chance.

Tier 2: Move-driven ground bounce

Only specific moves tagged ground_bounce cause a pop when they end a juggle or connect on a downed target. The ender explicitly trades damage or meter for conversion. This is the Street Fighter 6 model for many heavy normals and certain specials. Designers control which routes exist; neutral resets stay intentional.

Tier 3: Slam bounce with OTG bridge

A heavy slam drives the defender into the floor, applies a high pop, and opens a one-frame OTG window before relaunch — linking OTG sweeps into aerial follow-ups. Popular in tag fighters and combo-heavy action games. Must be budget-capped: one OTG bridge per combo is usually enough.

Tier 4: Bounce into wall carry

Floor pop includes horizontal velocity toward the nearest wall so the next hit can trigger wall bounce. Powerful for corner carry but requires shared bounce budget across floor and wall to prevent pinball infinites.

Height, timing, and physics math

Ground bounce feel is mostly vertical impulse and hitstun, not full physics simulation. Document these parameters per bounce tier:

Pop impulse (vy0) — initial upward velocity in pixels/frame or m/s; typical range 8–18 px/f for fighters at 60 fps.
Gravity during pop — often higher than normal juggle gravity so pops are snappy, not floaty.
Peak height target — design in character heights: floor pop should peak below jump height so anti-airs do not dominate every bounce route.
Bounce hitstun bonus — +N frames on pop connect so the attacker's fastest air move can link; if bonus + remaining decay < move startup, the route is a dead zone.
Invulnerability tail — brief post-pop invuln prevents the same frame from re-hitting twice (double-contact bugs).

Worked example: defender falls at vy = −14 px/f. Floor pop applies vy0 = +11 px/f with juggle gravity 0.55 px/f². Time to peak ≈ 20 frames; peak height ≈ 110 px. If attacker's j.H has 9f startup and must connect at peak −5 px, the relaunch window is roughly frames 8–16 after pop — tight but learnable. Log these windows in training mode.

State clock vs animation

Like OTG windows, ground bounce must fire on state entry when the floor collision registers, not when a fall animation touches the ground visually. Rollback fighters need serialized bounce counters and pop impulse on the wire. Animation lag between hit and floor contact causes desync if bounce timing follows clips.

Integration with juggle, OTG, and knockdown rules

Juggle budget coupling

Ground bounce should consume juggle resources. Typical policy:

Each floor pop decrements bounce budget (often 1–2 per combo).
Hitstun decay continues through pop — do not fully refresh unless the bounce ender pays meter.
When budget hits zero, next floor contact is untechable fall or hard knockdown with no pop.
Damage scaling applies a floor-bounce tier penalty (e.g. 0.85× per pop) so extended routes pay in output.

OTG interaction

Three valid models — pick one per game, not all at once:

No OTG on bounce — pop goes straight to relaunch; simplest for rollback.
OTG bridge — one OTG-class hit between pop and air relaunch; consumes OTG token separate from prone oki.
Bounce replaces OTG — move that ground-bounces cannot also OTG prone targets; prevents redundant low tools.

Knockdown type gates

Hard knockdown enders should not ground-bounce unless explicitly tagged (super routes). Soft knockdown juggles are the default bounce source. If combo resets re-open juggle state, reset bounce budget too or players loop floor pops forever.

Harbor Brawl refactor

Before the refactor, three problems stacked:

OnFloorContact callbacks lived on individual move scripts; some launchers called bounce, others called HKD with identical VFX.
No shared bounce counter — QA found a two-pop infinite using wall carry plus unregistered floor skid.
Pop height varied with horizontal velocity, so corner routes bounced higher than midscreen routes for the same ender.

The combat team shipped:

Central FloorBounceController on defender state: tier, impulse, budget decrement, OTG bridge flag.
Per-combo bounce_remaining (default 1, max 2 with meter ender).
Fixed pop height per tier independent of horizontal speed; wall carry applied as separate velocity bonus on tier-4 enders only.
Training overlay: bounce arc ghost, budget counter, relaunch link success rate.

Metrics after one balance pass: floor-to-air conversion 12% → 38%; average combo damage on bounce routes +9.4% (scaling penalty capped runaway); hard-knockdown neutral share unchanged — HKD enders still dominate when players want oki, not damage.

Technique decision table

Scenario	Prefer	Avoid
Anime fighter with long combos	Move-driven bounce on heavy enders + 1–2 bounce budget	Passive pop on every juggle floor touch
Grounded neutral-focused fighter	Hard knockdown enders; bounce only on EX/super routes	Default light-chain floor bounce
Tag / assist combo systems	Slam bounce with OTG bridge for tag relaunch	Unlimited floor+wall bounce without shared budget
Rollback online	State-entry pop impulse + fixed hitstun bonus	Animation-synced floor skid timing
Teaching new players	Training mode bounce arc + link helper	Identical VFX for bounce vs HKD with no UI distinction
Corner carry design	Tier-4 ender with horizontal bonus toward wall	Passive pop that always sends toward corner from midscreen
Competitive balance	Scaling penalty per pop; meter cost on second bounce	High-damage bounce ender with no recovery cost

Pitfalls

Passive pop on every floor touch — removes knockdown ender identity; optimal play never chooses HKD.
Bounce without budget — floor+wall loops become infinite with decay math alone.
Velocity-scaled pop height — corner damage exceeds midscreen for identical inputs; feels unfair.
Animation-based bounce timing — rollback desync and hitstop bugs.
OTG bridge without token limit — sweep into relaunch every knockdown breaks defensive knockdown value.
Pop too high — every bounce route becomes anti-air bait; low profiles and sweeps dominate follow-ups.
Identical VFX for bounce and HKD — players cannot learn which enders reset neutral.
Forgetting scaling — bounce routes out-damage HKD oki without penalty, shrinking defensive knockdown value.

Production checklist

Define bounce tiers (passive, move-driven, slam+OTG, wall-carry) in design doc.
Tag ground-bounce enders in move data; never infer bounce from animation names.
Centralize floor contact in one controller with state-entry timing.
Set per-combo bounce budget; share counter with wall bounce if both exist.
Apply damage scaling penalty per floor pop; log in combo HUD for balance.
Couple pop to juggle decay — verify fastest air linker connects at peak window.
Gate hard knockdown enders: no bounce unless explicit super/EX flag.
If using OTG bridge, consume separate OTG token; max one bridge per combo.
Fixed pop impulse per tier; decouple height from horizontal velocity.
Training overlay: bounce arc, budget remaining, relaunch success/fail reason.
Rollback test: serialize bounce count, pop tier, and impulse each frame.
Balance metrics: floor-to-air conversion rate, bounce-route damage share, HKD oki rate.

Key takeaways

Ground bounce pops defenders off the floor into brief air state for combo extension.
It is not OTG (hitting prone) and not wall bounce (horizontal geometry).
Move-driven bounce with a per-combo budget preserves knockdown ender identity.
Harbor Brawl floor-to-air conversion rose from 12% to 38% after a unified bounce FSM.
State-clock pop timing and fixed impulse per tier are mandatory for rollback safety.