Trauma causing temporary unconsciousness: what happens physically?

I am a fan of combat sports such as boxing and martial arts. In competition a person might get hit and temporary lose consciousness, often for a fraction of a second before they regain their senses. I would like to know what is happening on a physiological level when this occurs.

1. What is actually happening that forces the person to go unconscious?
2. Some people have "iron chins" and never have this happen, even when they get hit. Why could this be?
3. How strong of an indicator is this loss of consciousness for long-term damage?
4. Say Albert and Richard both get hit with an equal amount of force. Albert loses consciousness temporarily and Richard does not. Does this mean Albert experienced a greater degree of trauma than Richard?

Thank you for any help. Sorry if I posted this in the wrong forum, please move if necessary.

 

To question #1:

Everything I've read implicates the thalamus as the critical structure whose function is being disrupted when people lose consciousness due to trauma, seizure, disease.

en.wikipedia.org/wiki/Thalamus

Although the shape of the whole brain is distorted by the kind of impact a hard punch represents, it is specifically distortion of the thalamus which probably causes temporary unconsciousness.

However, the thalamus itself is regulated by the reticular formation of the brainstem:

So, trauma to one, the other, or both at once, could cause temporary unconsciousness.

Apropos: I can't recommend any activity that involves blows to the head:
en.wikipedia.org/wiki/Dementia_pugilistica