Athletics - Grapple

Grappling involves any type of fighting where one attempts to physically control the posture and momentum of another character. Grappling is an intricate fight filled with many positions, and just as many techniques to advance and defend those positions, as well as various submission holds, chokes, and pinning maneuvers. While some player knowledge of these positions, what they are called, and how they work can add fun and immersive details to Athletics - Grapple checks, it is hardly a pre-requisite to using this supplement, especially if your GM has knowledge the fundamentals of grappling.
For the purposes of combat encounters, we abstract grappling into three primary positions: Neutral Position, Advantageous Position, and Superior Position. The character with the better position (The advanced or Superior Position) they are considered to be the "top" while the being effected by the negative effects of the grapple is the "bottom".
You may only make an Athletics - Grapple check when you are engaged with a single adversary. From there, a character may make an opposed Athletics - Grapple check as an action to begin a grapple their opponent and improve their position. On a success, the active gains the Neutral Position and neither the attacker or the defender has any advantage from this position (unless positive or negative dice results let one character gain an Advanced or Superior position) but neither of two characters can use the "move" manuever to change their position on the battlefield. From now until the grapple is broken, the two of them are considered to be "grappling".
From there, a character may make an opposed Athletics - Grapple check as an action to begin a grapple and improve their position. A successful opposed Athletics - Grapple check improves a character’s position from Neutral to Advantageous, or Advantageous to Superior depending on the results. Subsequent checks can improve this position further. 
Conversely, if your character is the victim of a grapple, and an opponent already has an Advantageous or Superior position, you may make an opposed Athletics - Grapple check to escape. Success at an opposed Athletics - Grapple check to escape reduces a Superior Position to an Advantageous one, or an Advantageous Position to a Neutral one. It can also move from a Neutral Position to a total escape, where the character has broken the grapple and may move from the opponent as normal.
While in an Advantageous Position, the top character adds bto all Brawl checks against the bottom character, while the bottom character adds b to all Combat checks they make against the top character.
While in a Superior Position, the top character adds bb to all Brawl checks they make against the bottom character, while the bottom character adds bbmaneuver
Attacking Grapplers
While grappling is relatively simple when it’s only between two fighters, things can get more complex when additional enemies or allies join the fray. The flurry and chaos of two grappling opponents makes additional combatants a liability for both parties. If two characters are grappling and a third character moves to engaged the two grapplers - the grapple is immediately broken and both of the grapplers are considered to be at engaged range.
As normal, if two characters are engaged, making an attack with a ranged weapon at an engaged target upgrades the difficulty of the attack once. However If two characters are grappling, firing a ranged weapon at a grappling target upgrades the difficulty of the attack twice instead. If d is generated during the attack, the attack hits an ally (this might be in addition or instead of the actual target, depending on the results of the check). This may be further impacted by the rules for attacking a prone target or attacking while prone.
Improve Position
Once engaged with an opponent in combat, a character can make an opposed Athletics - Grappling check to get into an advantageous position. If a character already has an Advantageous Position, they might make an Improve Position action again to attempt to gain a Superior Position.
Escape
The Athletics - Grappling skill can also be used to escape a bad position when grappling. Make an opposed Athletics - Grappling check to escape a submission, restraining hold, or an enemy’s Advantageous or Superior position, or escape a grapple altogether. A successful check reduces an opponent’s position one step from Superior to Advantageous, Advantageous to Neutral, or Neutral to disengaged.