Overhand Chop (Ex): At 3rd level, when a two-handed
fighter makes a single attack (with the attack action or a
charge) with a two-handed weapon, he adds double his
Strength bonus on damage rolls. This ability replaces
armor training 1.
Weapon Training
Does this apply when making attacks of opportunities?
No.
The 'attack action' called out is a specific type of standard action. So overhand chop can only be done on your turn when using your standard action to make a single attack (as opposed to making a full attack) - or when charging.
Anyone have a link to how to best define "the attack action". I'm aware there are many kinds of weirdly worded actions that involve attacks, and I should probably educate myself on what makes them different.
The "Attack Action" and a "Melee Attack" might seem close, but they are not the same thing. The Attack Action is an attack that is made as a Standard Action. A melee attack is an attack that can be made as an Attack Action (a Standard Action) or as part of a Full-attack Action (a Full-round Action).
Combat Maneuvers such as Disarm, Sunder, and Trip are clear to note they are "in place of a melee attack". So you can perform multiple attempts of these during your turn.
In fact a Sunder FAQ suggested removing the text "as part of an attack action in place of a melee attack" and replacing it with just "in place of a melee attack" because the wording could be confusing as to whether you could perform multiple Sunders in a Round or not.
Source on this page.
So bbangerter is correct.
It might have been less confusing if the ability read "(as a standard action or as part of a charge)" similarly to how Overrun is worded.
Cool info:
Charging Hurler allows you to use Overhand Chop with some thrown weapons.
As long as it's a two-handed weapon and you can throw it, then yeah. :)