Open Fist - This weapon is an Open Fist. A model can use a weapon with an Open Fist to make some power attacks:

• The following model types (warbeasts, warjacks, horrors, and monstrosities) can use it to make a throw power attack.
• Gargantuans and colossals can use it to make either a throw or a power strike power attack.
• Warjacks need to have at least one non-crippled open fist if they want to perform one of the aforementioned power attacks. (The other model types don't suffer crippled systems).

Rules Clarification : Open Fist  (aka, Power Attack Throw)     (Edit)

• Throw ( Edit )
  • See also the Throw article for a recap of the core Throw rules.
  • If a model is somehow thrown at itself (which can happen with Durst1's feat) it would not move, it would be knocked down, and it would take a standard power attack damage roll but it would not take an additional die for colliding with itself. (Infernal Ruling)
  • Because you move the target model between the attack roll and the damage roll, you can get different buffs applied to the two rolls. For instance, if you throw the target in or out of a Flanking model's melee range.

• Incorporeal vs Slammed/Thrown models ( Edit )
  • Incorporeal models cannot be moved by someone trying to slam them.
  • Slammed models can move through Incorporeal models.
    • If they have enough movement to get past them, no dramas.
    • If they land on them, you move the Incorporeal model out of the way as per the Rule of Least Disturbance.
    • If the Incorporeal model cannot be moved (i.e. it's a flag) then you move the slammed model out of the way, also by the rule of Least Disturbance.
    • For the purposes of Collateral Damage, only the model(s) you contacted before you applied the rule of Least Disturbance count as contacted.
  • The same logic applies to Throws.

• Collateral Damage
  • Collateral damage cannot be boosted and is not considered damage from an attack or model. Refer page 33 of the 2021.08 version of the rules pdf. As a result:
    • It doesn't trigger stuff that relies on being hit by an enemy (such as Shock Field) or damaged by an enemy (such as Vengeance).
    • It doesn't get bonus damage from stuff that adds to a model's damage roll (such as Signs & Portents or Prey).
    • It doesn't matter if the attacker has crippled weapon systems or aspects.
• Throw - Power Attack
  • When you make a Throw Power Attack, no other abilities of the Fist weapon (such as Chain Strike) are applied unless they specifically mention Throws. (Locked Thread)
  • If you do a Power Attack Throw and you choose to throw the target directly away, no deviation is rolled to determine the final position of the model. (Locked thread)
  • A model that cannot be targeted by melee attacks (such as Una2's feat) cannot have models thrown at them, either. (Infernal Ruling)
  • Since throwing Model [A] at Model [B] involves making a melee attack roll vs Model [B] which is out of your melee range, it technically breaks a whole bunch of core rules. (Infernal Checking)
  • Even though you make a "melee attack roll" vs Model [B] you don't actually make a melee attack vs it. Also, the damage it suffers is from Collateral damage, not from the original attack. So you can't trigger stuff like Snacking from damage you did to Model B.