Neutral

Neutral is when both players can act freely. The term is used in contrast to situations where there's a frame advantage or okizeme. It's usually not used in contrast to a health advantage, resource advantage, or positional advantage from the wall.

Neutral most often occurs when both players chose a movement option in pressure. Since these options are strong, this happens a lot, so being comfortable in neutral is a key skill.

Goal

The goal of neutral is to enforce your mixups and prevent your opponent from doing the same. To do this you have to:

Interrupt your opponent's attacks with your own.
Use movement to make your opponent's attacks whiff, then whiff punish them.
Use movement so your attacks will connect.

Flow

The simplest way of thinking about the flow of neutral is as a rock-paper-scissors between three options:

Waiting out of the opponent's range, which beats an attack being thrown out.
Throwing an attack out into empty space (keepout, sometimes called okiwaza), which beats running in and doing a mixup.
Running in and doing a mixup, which beats waiting.

The first step to a robust neutral plan is finding suitable attacks for these options:

Whiff punisher: Ideally a fast, long range move with good reward on hit.
Keepout: Ideally a safe move with good reward on hit or counter hit.
Mixup: A combination of a low and a safe-on-block mid, both of which ideally have good reward on hit.

Pokes

Things get more complicated when we start considering pokes. Unlike more high reward options, pokes can be thrown out into empty space without the risk of being whiff punished, which allows them to largely dominate all of the aforementioned options. Waiting around won't punish them, and attacking gets interrupted.

The big weakness of pokes in neutral is that despite being faster than higher reward attacks, they don't always win. It's possible to throw a poke out at an unfortunate timing and have it be interrupted by a slower attack or incidentally whiff punished by a keepout move (i.e. not whiff punished on reaction).

As such, even the safest attacks carry an inherent risk in neutral. Although pokes win more often than not, their low reward compared with this inherent risk may not be worth it. The degree to which pokes are dominant largely depends on how well players are able to lock out other options with whiff punishment.

Finding good moves

Although the broad flow of neutral is similar for all characters, the details change based on their moves' properties.

Whiff punisher

Ideally a whiff punisher is fast and doesn't require a motion input, is mid, safe-on-block, and has long range and big payoff on hit. Of course no whiff punisher is all of these things, so you must take care to consider and account for where each of yours are lacking.

Slow whiff punishers don't work against faster recovering moves.
- Motion inputs slow down the move, even for the best players.
High whiff punishers don't work against crouching whiffs.
Unsafe whiff punishers are dangerous if you misjudge the whiff.
Shorter range whiff punishers require finer care and attention to spacing.
Whiff punishers with lower payoff won't discourage opponents from whiffing as much.

Keepout

There's a blurry line between what makes something a poke, mixup, approach, or keepout move. In the context of keepout we're throwing these moves out into the wind. There's a chance they'll whiff and a chance they'll be interrupted—but also a chance of the same in your favor. The qualities we're looking for with these moves are:

Ability to win duels: If both players attack at the same time, who wins? The most influential thing here is the startup speed, but high crushing and not being a high (i.e. evasion, states, and hit levels) are also valuable.
Payoff on wins: If the move hits or counter hits, how much damage do you get?
Chance to whiff: When the move is thrown out, how likely is it to whiff? This is influenced by its range and tracking, i.e. the quality of its hitbox.
Difficulty to whiff punish: If the move whiffs, how likely is it to be punished? This is primarily influenced by the total time the move takes, i.e. startup plus recovery, but is also influenced by where and how the move recovers. A move recovering in crouch can't be whiff punished by highs, and a move recovering further away can only be whiff punished by long range moves. You can also make things tricky with cheese by e.g. whiffing a move with string extensions, making your opponent's job of reacting properly harder.

Moves with more than one of these qualities are particularly strong. For example:

Lee's b+4 has massive payoff on wins with a nasty counter hit combo. Its fast recovery and option to fall back with the HMS transition make it incredibly difficult to whiff punish. And its great hitbox makes it unlikely to whiff, unless the opponent stays so far away that they can't whiff punish it anyway.
Generic d+4 is fast and high crushes, so it almost always wins duels. It also has good range and tracking, so it's unlikely to whiff. And it also has fast recovery and recovers crouching, making it hard to whiff punish.

While there's nothing inherent to moves done from a dash or run that makes them better than any other move in neutral, these moves are often strong in their own right, but their input limits their usefulness to this context. You can just as well complement a dash with any other move.

Keep in mind that if all of our keepout moves are mids, then an opponent can approach very easily with a dash block. Having lows that also work well as keepout buttons can address this. To some degree we want to do keepout and mixups at the same time. For example, generic d+3 (such as Kazumi's) might look pretty unassuming, but it has a lot of the above qualities: wins duels with its speed and high crush, okay payoff on wins (12 damage), unlikely to whiff due to its range, and hard to whiff punish due to its low recovery.

Mixup

A move used primarily for mixups is intended to be complemented by movement. So rather than being concerned with the chance to be interrupted or whiff, the chief concern is how good these options are against guard. (Of course ideally you'd have full-screen, impossible to interrupt or whiff punish mixups, but you won't find many moves that fit the bill there.)

As such, the moves to consider here can be narrowed down a lot. Find the lows and safe-on-block mids with the highest payoff on normal hit. For characters with good throws or mixup stances consider those as well. Think of these as the end goal of neutral.