I was reading the article ‘Karate Training& What to Know About Fighting‘ by Kyan Chotoku and what he had to say about karate applications seemed interesting. Just look at this passage.
"Even if the opponent seizes your foot or leg, you can take advantage of it by quickly stepping down and into him, reducing the risk of injury."
For this suggestion I bring personal memories to mind.
The first one I worked out was is anticipating someone was preparing to grab my kick, by forcefully placing the foot down, not continuing in the kicking motion, can become a forceful step forward to accompany a strike at the same time, which is also a force enhancer.
Another example came from my time training with Tristan Sutrisno. He once showed me an Indoneasian answer to someone grabbing your foot, There upon forcefully stepping down through that grab, through that motion with the foot movement. Which draws them closer at the same time as they try to continue their attempted hold. Which of course makes it easier to counter-attack their grabbing motion.
Both are well within Isshinryu parameters. Of course the speed at which Shimabuku Sensei delivered his kicks, really did not allow anyone to grab them either.
I know because when I tried to ‘grab’ those kicks with screen capture, I could not do so, only getting the retraction of the foot.
That is likely the real Shimabuku Tatsuo lesson.
This the best I could do with my screen captures. I believe this motion might be used in a similar fashion to break free of a grab.