It is a very complex question because defensiveness is a complex form of behavior caused by different triggers and manifested in different ways.
If I understood correctly, you are interested in defensiveness which is defined as:
- the quality of being anxious to challenge or avoid criticism;
- too quick to protect yourself from being criticized;
- acting to ward off their having to experience some unwanted feeling or admit responsibility for some disowned act.
Outwardly, it usually as lack of accountability and tendency to avoid consequences.
But the inner mechanism is actually a very pronounced sensibility to comments people prone to defensiveness perceive as (negative) criticism.
However, these mechanisms I just mentioned can also CAUSE the defensiveness in other people.
People who grew up with demanding parents tend to be very sensitive to criticism and may be closed to the idea of discussion, thus acting defensively. So, if there are any indicators that a native might have had perfectionist and appearance obsessed parents, this could be a good reason to assume that he might have developed certain defensive mechanisms.
Traditionally, family we come from is represented by the 4th house, the Sun is the father and Moon the mother. The modern astrology connected the father to the 4th house and the mother to the 10th. So their rulers should be carefully examined.
Defensive behaviors might surface as the consequence of certain relationships too. So when a native gets in touch with manipulative and controlling individuals or overly critical people he might show defensive traits.
Same goes when dealing with people who never accept their responsibility and shift blame or when dealing with people who have binary way of thinking and who are, of course, always right. Having family members, colleagues or friends who purposefully hide certain information may also provoke defensive behaviors.
Defensiveness is about relationships and depending on their nature, the reasons and manifestations can be different.
Relationships with siblings and neighbors are represented by the 3rd house, with partners by the 7th, your friends by the 11th, colleagues by the 6th… so when looking for possible defensive behaviors, one should take into account these houses and their rulers.
So it is difficult to single out a couple of aspects and say that they are indicators of defensiveness.
I’ve met people who have difficult placements of Pluto (7th house affecting their partnerships and the way they relate to others, always feeling “under attack”) forming stressful aspects with other planets (opposition Jupiter, conjunction Mercury affecting their values and reasoning) who are always blaming others and are practically impossible to talk to reasonably.
I’ve also seen people with pronounced victim psychology in their charts, who seem more passive than the previous example, but they are very sensitive, stubborn and close-minded. Their Pisces and Neptune are very pronounced, clouding their reasoning, making them highly sensitive.
I would say that defensiveness rises from severe sensitivity to criticism, perfectionism and in some cases clouded judgment. But it is mostly a question of one’s ego being hurt than their inability to clearly see the situation.
Hope this helps.