Squeezing comes about when the space a creature takes up on a combat grid is larger than a spot it wishes to go through. For example, if you have a person taking up a normal two meter by two meter square they can clearly squeeze through a one meter wide opening. What happens to them when this is taking place? How does it affect their movement and combat capabilities? This question also arises when a creature taking up a chunk of space two squares wide tries to squeeze between two enemies who have one empty space between them. Surely the large creature can get itself through a space two meters wide, but how does this occur exactly?
I want to have the rules cover this circumstance but every time I try to write something up it ends up being half a page. I really want to avoid gigantic blocks of text because I know every time I see such things in a system somebody else wrote I shake my head and just make something up. It simply isn't fun to spend ten minutes reading a complicated section of rules several times to make sure you understand it when it will only apply for a few moments, especially when it will come up very seldom. Any rules surrounding something that comes up constantly or which is integral to the system have a lot more leeway of course; some rules you just have to figure out. When something is situational or niche though it simply must be simple and quick to adjudicate or you might as well not write it.
As as example of this here we have Heroes By Trade rules about grabbing another combatant followed by Pathfinder's rules. Note that the Pathfinder rules listed are not nearly comprehensive and several more large entries are required. To actually understand the whole thing you should probably visit a page especially designed to let you understand grappling, like this one.
Heroes By Trade rules:
Anyone can use a Maneuver against an enemy within their reach by declaring which Maneuver they are using and making a Physical Hit Roll. No weapon properties are added for this roll.
Grab: The target is Immobilized for 1 round if the attacker stays adjacent to it. Using a weapon with the Grab property allows the Hit Roll for a Grab to be made at advantage. A Grab can only be made against an adjacent opponent regardless of either combatant’s reach. To make a Grab the attacker must either have a free hand or be using a weapon with the Grab property.
Immobilized: You are held in place. You may not leave your current square voluntarily or otherwise.
As a standard action, you can attempt to grapple a foe, hindering his combat options. If you do not have Improved Grapple, grab, or a similar ability, attempting to grapple a foe provokes an attack of opportunity from the target of your maneuver. Humanoid creatures without two free hands attempting to grapple a foe take a –4 penalty on the combat maneuver roll. If successful, both you and the target gain the grappled condition (see the Appendices). If you successfully grapple a creature that is not adjacent to you, move that creature to an adjacent open space (if no space is available, your grapple fails). Although both creatures have the grappled condition, you can, as the creature that initiated the grapple, release the grapple as a free action, removing the condition from both you and the target. If you do not release the grapple, you must continue to make a check each round, as a standard action, to maintain the hold. If your target does not break the grapple, you get a +5 circumstance bonus on grapple checks made against the same target in subsequent rounds. Once you are grappling an opponent, a successful check allows you to continue grappling the foe, and also allows you to perform one of the following actions (as part of the standard action spent to maintain the grapple).
Move: You can move both yourself and your target up to half your speed. At the end of your movement, you can place your target in any square adjacent to you. If you attempt to place your foe in a hazardous location, such as in a wall of fire or over a pit, the target receives a free attempt to break your grapple with a +4 bonus.
Damage: You can inflict damage to your target equal to your unarmed strike, a natural attack, or an attack made with armor spikes or a light or one-handed weapon. This damage can be either lethal or nonlethal.
Pin: You can give your opponent the pinned condition (see Conditions). Despite pinning your opponent, you still only have the grappled condition, but you lose your Dexterity bonus to AC.
Tie Up: If you have your target pinned, otherwise restrained, or unconscious, you can use rope to tie him up. This works like a pin effect, but the DC to escape the bonds is equal to 20 + your Combat Maneuver Bonus (instead of your CMD). The ropes do not need to make a check every round to maintain the pin. If you are grappling the target, you can attempt to tie him up in ropes, but doing so requires a combat maneuver check at a –10 penalty. If the DC to escape from these bindings is higher than 20 + the target's CMB, the target cannot escape from the bonds, even with a natural 20 on the check.
If You Are Grappled: If you are grappled, you can attempt to break the grapple as a standard action by making a combat maneuver check (DC equal to your opponent's CMD; this does not provoke an attack of opportunity) or Escape Artist check (with a DC equal to your opponent's CMD). If you succeed, you break the grapple and can act normally. Alternatively, if you succeed, you can become the grappler, grappling the other creature (meaning that the other creature cannot freely release the grapple without making a combat maneuver check, while you can). Instead of attempting to break or reverse the grapple, you can take any action that requires only one hand to perform, such as cast a spell or make an attack with a light or one-handed weapon against any creature within your reach, including the creature that is grappling you. See the grappled condition for additional details. If you are pinned, your actions are very limited. See the pinned condition in Conditions for additional details.
Multiple Creatures: Multiple creatures can attempt to grapple one target. The creature that first initiates the grapple is the only one that makes a check, with a +2 bonus for each creature that assists in the grapple (using the Aid Another action). Multiple creatures can also assist another creature in breaking free from a grapple, with each creature that assists (using the Aid Another action) granting a +2 bonus on the grappled creature's combat maneuver check.
Grappled: A grappled creature is restrained by a creature, trap, or effect. Grappled creatures cannot move and take a –4 penalty to Dexterity. A grappled creature takes a –2 penalty on all attack rolls and combat maneuver checks, except those made to grapple or escape a grapple. In addition, grappled creatures can take no action that requires two hands to perform. A grappled character who attempts to cast a spell must make a concentration check (DC 10 + grappler's CMB + spell level), or lose the spell. Grappled creatures cannot make attacks of opportunity.
A grappled creature cannot use Stealth to hide from the creature grappling it, even if a special ability, such as hide in plain sight, would normally allow it to do so. If a grappled creature becomes invisible, through a spell or other ability, it gains a +2 circumstance bonus on its CMD to avoid being grappled, but receives no other benefit.
Pinned: A pinned creature is tightly bound and can take few actions. A pinned creature cannot move and is flat-footed. A pinned character also takes an additional –4 penalty to his Armor Class. A pinned creature is limited in the actions that it can take. A pinned creature can always attempt to free itself, usually through a combat maneuver check or Escape Artist check. A pinned creature can take verbal and mental actions, but cannot cast any spells that require a somatic or material component. A pinned character who attempts to cast a spell must make a concentration check (DC 10 + grappler's CMB + spell level) or lose the spell. Pinned is a more severe version of grappled, and their effects do not stack.