The neutralization of attacks is a primary concern with taijiquan.
How though is one to neutralize extreme yang type energies?
The answer is of course in balance, extreme yang is defeated by extreme yin.
Yang is full and yin is void.
Consider a car speeding towards you as an example of extreme yang.
What is the ideal technique?
The answer is: empty space.
If we consider the teaching of the 13 postures also we know that there are preferred directions.
When extreme yang moves forward the reciprocal answer is moving right with extreme yin, this creates empty space and positions one out of the way.
You see, it is not possible to rollback a car. Nor are all human attacks able to be neutralized.
Some attacks can be very powerful and very fast. There are two ways to deal with them, the first is anticipation of the attack and preemptive defensive attack. This is the defense using offense principal. The second method of dealing with a powerful fast attack is to move out of the way into a position that has the advantage. If someone moves forward you move right, they have to turn left or move left to deal with someone having moved right. These position aspects of the 13 postures are almost like the game: paper, rock, scissors. Except we must keep in mind that some of the outcomes are dealt with not by a reciprocal energy, but by a lack of one, at least in the case of extreme yang nature attacks.
If two opponents or opposing energies (duifangs) face each other their interaction can be described by position/motion and energy. The system allowing this comprehension is the 13 postures. It allows those who practice it to be able to respond to the movement of the duifang in a way that can seem by some to be magical or based on some mystical energy, but the truth is that it is simple physics and cleverness that form the basis of the system. How it is used can vary, once comprehended the person who masters taijiquan can manifest the art in myriad ways including lethal, or non lethal. Taijiquan is neither a deadly martial art nor is it a non-deadly martial art, rather it is comprehension of the physics of violence in a physical manner that transcends the limitations of strength, speed and technique. This is not something that can be learned quickly.
There is a saying, in some taijiquan transmissions, that 3 years of kung-fu beats 10 years of taijiquan. This is because the skill set of taijiquan cannot be gained without much work and effort. However a practical skill set for fighting can be gained in 3 years using various strategies and techniques. For this reason many schools appear to supplement the taiji training with practices resembling Wing Chun or White Crane, focusing on attack and self defense skills while slowly building the real taiji skill set.
If someone learns what taiji is, they cannot use it. If they try to do it, they will only fail. Taiji is not done, rather it is like water, it has no intent of its own. It is undifferentiated and so can respond to anything, whereas having an intention is to have a distraction.