This video was shared with me by a friend in the USA. It’s largely about Roberto Duran's In-Fighting. What is observed is how, when close, he would use one hand to inform and control while hitting with the other.
The same observation was made about Kushanku (the man) whose methods form the basis of Tode Sakgugawa’s kata of the same name.
There is a document called ‘Oshima Hikki’ (Note of Oshima). This document details a ship running ashore in Oshima bay and includes interviews with the crew of that ship. In one of these interviews the captain of the ship tells of an extremely impressive grappling demonstration he witnessed that was given by Kushanku. The interview tells us that Kushanku was not a physically strong man and yet he defeated much stronger opponents with ease. We are also told that his methods involved placing one hand on the opponent whilst striking with the other hand.
Although this eyewitness was talking about Kushanku, the use of both hands is almost universal on all kata movements. The reason being that in civilian self-protection (the kind of violence that traditional karate addresses) people are very close to one another such that having hands held in an inactive guard is neither appropriate nor practical.
Fighting to escape from criminals obviously has a different objective and optimum methodology than out-boxing a skilled boxer in a ring, but the commonality of using the non-striking hand to facilitate the striking hand when “in fighting” / at close-range is something I’m sure you’ll find interesting.
All the best,