Can a character without natural attacks or improved unarmed strike use their unarmed strike to make a combat maneuver?
[RPG] Are combat maneuvers allowed with unarmed strike
combat-maneuverpathfinder-1eunarmed-combat
Related Solutions
Replacing a claw attack with an unarmed strike
Sorry, but no. Unarmed strikes use a weird hybrid of the rules for manufactured and natural weapons, but for the purposes of full-attacks, they work like manufactured weapons. That is, you get iteratives with them, but if you can only combine them with natural weapons by making those natural weapons secondary (−5 attack penalty, only ½Str to damage).
The first rule that you quote is specifically about spells and effects. A full-attack is not either of those.
Claws and lack of offhand unarmed strikes
Feral Combat Training does mean that anything from the monk’s unarmed-strike-improving class features can apply to natural weapons, and that can include the bit about never being offhand.
However, claws and other natural weapons are never “offhand” to begin with. The term “offhand” only applies when using two-weapon fighting, and that combat option does not interact with natural weapons (aside from the attack penalty, which applies to all attacks). So the fact that the monk class feature, combined with Feral Combat Training, says that natural weapons are never offhand does not do anything because that was already true.
Instead of “main hand” and “offhand,” natural weapons are either “primary” or “secondary.” These are different. When combined with manufactured weapons (or unarmed strikes) in a given full-attack, all natural weapons are secondary: they receive the −5 penalty and get only ½Str to damage. Neither the monk class nor Feral Combat Training does anything about treating them as secondary or removing or reducing the penalties for being secondary.
So whether you have Feral Combat Training or not, your full-attack using unarmed strikes is:
Unarmed Strike, Claw (−5), Claw (−5), Claw (−5)
If you have Feral Combat Training, the claws do benefit from the improved base damage dice of unarmed strike, however, even if they’re still stuck with ½Str to damage.
Two-Weapon Fighting, Feral Combat Training
If you are actually using two-weapon fighting, the provision about monks never having offhand unarmed strikes meaningfully applies only to the unarmed strike. It “applies” to the claws, but does nothing for them.
So, for example, if your two weapons are a sai and an unarmed strike, and you have the Two-Weapon Fighting feat, your attack routine would be:
Sai (−2), unarmed strike (−2), claw (−5), claw (−5)
The unarmed strike would add your full Strength to its damage, however. Note that I assumed that the sai took up one of your claw-hands. I did not wish to get into the debate about whether one can use two unarmed strikes as part of two-weapon fighting.
You didn’t ask, but about Flurry of Blows
All of the statements above about full-attack apply equally well to flurry of blows, except that you need Feral Combat Training to use natural weapons in a flurry at all, and flurry of blows cannot be combined with two-weapon fighting because of Paizo nonsense.
Personal recommendation
For the record, monks, natural attacks, and how they combine, these are some of the worst things in Pathfinder. The rules are confusing, complicated, and the result works very poorly. I suggest you save yourself a headache and just... not.
If you have the Improved Unarmed Strike feat, you do not get the -4 penalty.
When the game rules talk about being unarmed, they talk about not wielding a weapon. Improved Unarmed Strike means that you know how to handle yourself in an unarmed fight and in effect are Armed (are wielding a weapon) because you have a weapon on hand (even if it is literally just your hand) even though you aren't holding weapon. People without the feat are assumed to be unable to effectively handle themselves in a fight without a weapon.
Think of it as the difference between a regular person on the street, and a martial artist, or boxer.
Benefit: You are considered to be armed even when unarmed—you do not provoke attacks of opportunity when you attack foes while unarmed. Your unarmed strikes can deal lethal or nonlethal damage, at your choice.
Normal: Without this feat, you are considered unarmed when attacking with an unarmed strike, and you can deal only nonlethal damage with such an attack.
Best Answer
I assume you are referring to combat manoeuvres that can be attempted in place of a melee attack, namely trip, disarm, and sunder.
According to this FAQ on the Paizo website:
From this answer, it seems clear than an unarmed strike is considered a weapon that can be used for combat manoeuvres.
Sundering with a normal unarmed strike is not possible because because objects are immune to nonlethal damage. See Smashing an Object on this page.
Note, however, that an unarmed character does not threaten nearby spaces, so an unarmed character would not be able to make combat manoeuvres such as trip as an attack of opportunity. "If you're unarmed, you don't normally threaten any squares and thus can't make attacks of opportunity." See Threatened Squares under Attacks of Opportunity in the combat rules.