Choto Kyan Extracts from what to know about Fighting.
Translated by Patrick and Youkio McCarthy
I believe I have only seen two versions of this, and it has not been widely disseminated. It is worth the time to read.
5. During a fight pay close attention to defending the center-line and not be caught off balance by staring at the oponents feet or eyes. You must be especially careful not to get hit in the vital organs, grabbed or even have the testicles seized when attacked. Also, it is not always wise to use too much force in defensive technique as movement tends to become slower, which also reduces the possibility for quick reaction or taking advantage of an opportunity.
For one thing I was taught to focus on the opponent’s chin, where peripheral vision allows you to see the entire opponents actions. I was taught the eyes of an opponent might captivate your awareness.
6. If you sieze an opponent’s wrist, garment or arm, be certain to maintain a pliable strength at the time being prepared to exploit his reaction. This way you can maintain control of the opponent’s movement.
In practice we try to use light pressure controls over grabs for just this reason.
There is much more in “Motobu Choki Karate” by the McCarthy’s