Guide

Game just guard and perfect guard systems explained

Harbor Siege’s ranked duels rewarded passive defense. Hold back and block: chip damage ticked life down, guard posture drained slowly, and the only counterplay was a risky wake-up reversal after a knockdown. Skilled defenders had no reason to engage with blockstrings frame-by-frame — mashing block was optimal. After engineers added a just guard window — press block within three frames of each hit’s active frames — successful timing granted +4 frame advantage over a normal block, full chip immunity, and one meter pip, blockstring respect rate rose from 19% to 47% while average round length stayed flat. Defense became a timing skill, not a timeout.

A just guard (also called perfect guard, perfect block, or impact guard) rewards defenders for blocking at the moment of contact rather than holding guard early. It sits between passive hold-block and full parry systems: you still use the block input, but impact timing changes frame data, resource economics, and pushback. Without deliberate just-guard tuning, chip damage and guard-break meters punish turtles while offering no skill ceiling for players who read offense. This guide covers timing-window math, reward taxonomy, interaction with chip and posture, blockstring counterplay, meter coupling, the Harbor Siege refactor, a technique decision table versus hold-block-only defense, pitfalls, and a production checklist.

What just guard adds to hold-block

Standard block resolution is simple: if the defender is holding guard in the correct direction when an attack’s hitbox overlaps, apply blockstun, chip damage, guard-meter drain, and pushback. The attacker keeps frame advantage defined in the move’s frame data. The defender’s only levers are fuzzy guard timing, guard cancel routes, or eating the pressure until a gap appears.

Just guard inserts a second resolution path at impact:

Timing gate — block input must transition to “guarding” within N frames before or after the first active frame (common: 2–4 frames before impact through 1 frame after).
Modified blockstun — shorter stun or bonus advantage frames for the defender (e.g. normal block is −2; just guard is +2).
Chip immunity — zero life loss on that hit even if the move normally chips (see chip damage systems).
Reduced pushback — defender stays in range to counter or reset neutral instead of being pushed to corner escape distance.
Meter reward — partial super gauge, drive meter, or guard resource refill to fund reversals and EX options.
Feedback layer — distinct VFX, SFX, and hitstop so players learn timing by ear and screen flash.

The design goal is not to replace hold-block — holding guard must remain viable for beginners and reaction defense — but to create a higher ceiling for players who recognize blockstring rhythm and want to flip pressure without committing to a full parry whiff risk.

Timing window design

Window width is the primary balance knob. Too wide and just guard becomes mashable; too narrow and only robots use it in live play.

Common window models

Impact-only — block press must occur on the same frame as hit connection (1-frame effective window). Used in high-level anime fighters for expert expression; often paired with generous practice-mode overlay.
Pre-impact buffer — allow 2–3 frames before active if guard was not already held (encourages deliberate taps on rhythm rather than holding). Guilty Gear’s Just Guard family uses variants of this.
Release-then-press — require releasing block and re-pressing within the window (prevents holding block from ever counting as just). Harder but kills “hold and occasionally get rewarded” feel.
Per-hit re-just — each hit in a blockstring needs its own timed input; one success does not carry through the string. Raises skill ceiling on multi-hit pressure.

Author windows relative to your slowest and fastest blockstring cadence. If your fastest gap is 3 frames, a 4-frame just window that spans the gap lets defenders just once and counter with a 4-frame jab — verify that trade matches your damage and meter goals.

Frame advantage math

Define base block advantage A_block and just-guard bonus B_just. Defender advantage after just guard: A_just = A_block + B_just. Example: move is +2 on block, −2 on normal guard for the defender; just guard adds +4 → defender is +2 and can jab before the attacker’s next frame trap. Document per move class (light, heavy, special) whether B_just is flat or scaled — scaling prevents lights from becoming infinite counter loops.

Reward taxonomy and economy

Pick rewards that reinforce your combat loop. Stacking every bonus on one mechanic makes just guard mandatory; starving it makes the feature cosmetic.

Reward	Player feel	Risk if over-tuned
Frame advantage only	Clean, footsies-focused; rewards reads	Invisible to casual players without UI
Chip immunity	Direct counter to chip-lethal turtle kills	Nullifies chip-centric characters
Pushback reduction	Enables mid-screen counter without corner	Breaks spacing on zoning characters
Meter gain	Funds comeback supers and EX reversals	Defenders always have meter; offense feels unrewarded
Posture / guard heal	Reverses guard-break grind	Stalls guard break pacing
Automatic counterattack	Spectacle (parry-adjacent)	Overlaps dedicated parry; pick one primary riposte path

Harbor Siege shipped chip immunity + 4f advantage + 1 meter pip per just. Chip immunity was later removed on supers (still chips on just) so defenders could not ignore unblockable chip kill routes entirely.

Blockstring and mixup interaction

Just guard changes attacker/defender incentives in blockstring pressure:

Frame traps — gaps designed to catch mash become weaker if just guard turns a trap frame into defender plus. Attackers may need delayed frametraps or lows after wider gaps.
Shimmy throw — reduced pushback keeps defenders in throw range after just; attackers must respect throw after respected just guard.
High/low mix — just guard on standing block does not help against lows; maintain mixup layers so defense is not one-size-fits-all.
Chip strings — immunity on just shifts value from “block and die slowly” to “time the rhythm or take chip.” Document which moves are chip-eligible on normal block only.
Fuzzy guard — pair with fuzzy guard so delayed crouch block and just guard cover different threat timings.

Telemetry: log just-guard rate per move slot in blockstrings. If one light button is justed 60% of the time, its block advantage on normal guard is too negative or its animation telegraphs impact rhythm too clearly.

Implementation sketch

A production resolver typically extends block handling:

On block input edge, stamp last_block_press_frame.
On hit vs guarding defender, compute delta = impact_frame - last_block_press_frame.
If guard was already held for more than M frames, reject just (optional anti-hold rule).
If delta within [-pre, +post], flag JustGuard on the hit event.
Apply modified stun, chip multiplier (0), pushback scale, meter hook, and trigger feedback.
Emit combat event for replay and tutorial highlights.

Networked fighters must evaluate just guard on the authoritative simulation frame with the same input history used for input buffering. Display rollback corrections with the same flash as local just success to avoid “I justed on my screen” distrust.

Harbor Siege duel refactor (worked example)

Harbor Siege’s duel mode added just guard in a mid-season balance pass:

Window: 3f before first active through 1f after (4f total).
Hold disqualifier: if block held >8f before impact, normal block only.
Bonus: +4 frame advantage, 0 chip, 75% pushback, +1 meter pip.
Supers: still chip 25% on just; chip-lethal routes preserved.
Training: blockstring rhythm mode with impact metronome and just flash.
Accessibility: optional 5f window in casual queues only.

Blockstring respect rose 28 percentage points; chip KO rate fell 11%; survey scores for “defense feels skillful” rose from 3.1 to 4.2 / 5 without increasing average match duration.

Technique decision table

Approach	Best for	Weak when
Just guard on block input	Fighters, duel brawlers, chip-heavy meta	Overlaps parry if both use timing + big reward
Hold-block only	Casual accessibility, simple AI	High-level defense lacks expression; chip turtles
Full parry / reflect	Soulslikes, cinematic counters	Whiff penalty too harsh for 60fps PvP
Guard break / posture only	Slow tactical duels	No moment-to-moment skill spike on defense
Drive parry (hold + drain)	Unified meter systems with rush/impact	Different skill test than impact-tap just guard
Harbor-style layered just	Ranked fighters with chip and blockstrings	More tuning surface; needs training mode support

Common pitfalls

Window too wide on lights — every mash becomes just; offense collapses.
Hold-block counts as just — removes timing skill entirely.
Full chip immunity on all moves — deletes chip-lethal character identity.
No feedback — players cannot learn rhythm without VFX/SFX.
Advantage high enough to infinite — jab loops after every just; cap bonus per string.
Ignoring lows and throws — just guard on stand block only; document coverage.
Netcode desync on just flag — authoritative frame must match rollback reconciliation.
AI always justs — bots need reaction delay tables, not perfect impact timing.

Production checklist

Define pre-impact and post-impact frame window per platform build.
Specify hold disqualifier threshold if tap-only just is intended.
Document per-move block advantage, just bonus, and resulting defender advantage.
Set chip multiplier on just (0 for normals, partial for supers if desired).
Scale pushback separately for normal block vs just guard.
Wire meter or posture rewards with per-round caps.
Author distinct VFX, SFX, and hitstop for just success.
Add training mode metronome and per-hit just success rate display.
Log just rate per move and per blockstring in combat telemetry.
Regression-test frametraps after just bonus patches.
Validate rollback authority matches local prediction feedback.
Document interaction with guard break, chip lethal, and throws in combat spec.

Key takeaways

Just guard rewards blocking at impact timing — not replacing hold-block but adding a skill ceiling on frame data and resources.
Window width, hold disqualifiers, and per-hit re-just rules determine whether the mechanic is expert-only or broadly learnable.
Chip immunity and frame advantage are the strongest anti-turtle levers; tune supers and pushback so character roles stay distinct.
Harbor Siege blockstring respect rose 28 points after a 4f just window with meter reward and super chip exceptions.
Pair just guard with mixup layers (lows, throws, frametraps) so one defensive option does not answer every attack.