Quote Originally Posted by Darg View Post
You can't set the condition to "when they take the charge action." Characters don't understand rules concepts. The conditions need to be in world valid such as the target attacking you. Thus they finish the movement of the charge, but because you readied an action you get to act before the attack. Otherwise you'd never be able to set a weapon and benefit from it because they'd always be out of range when you attack.
I think it needs to be able to occur mid-action and specify the "special attack" for Setting against a Charge to work due to the minimum range on the Longspear and the text in question only giving double damage "If you use a ready action to set a [weapon] against a charge". But given how Ready works, doing this should technically need you to properly define at which point you interrupt. Which in the Sidestep case is some distance they've committed to their direction and in the Set vs. Charge case when they start to be in reach.

Incidentally, it also seems that Charging doesn't prevent Attacks of Opportunity from anyone, which means that Reach weapons with the usual "minimum range" clause can technically make an AoO if the enemy closes within it. No matter that Longspears are very nearly exactly the opposite of what this makes sense for.