read your posts with Ken, its more like ken and you agreeing on activation.
If you have a skill that is mental or internal, i don't believe you have it on all the time. So the skill must be turned on and off, thereby being activated when it's needed for use and deactivated when not in use. You say its just happens naturally, I think you mean it works effortlessly or yukimura. It sounds like the yips techniques requires no energy and just a uses mere thought. could be true i for one don't believe mental techniques are so easy. its a difference of opinion.
I believe is that yips has to be directed to an opponent. this is not a technique like hitting a super serve or super shot, there fore it must be turned on or activated. If there is no mental projection, or mental direction to a specific person, then people in the audience would get yips on accident. also direction/projection usually requires focus and requires mental stamina.
Yukimura doesn't say he wants to embarrass his opponent true, (I am speculating about his play-style (I can admit I may be wrong ) going by his actions,
My question is does an expert player need to keep hitting the ball at an opponent who is near helpless to return the ball?
Yukimura can lob shots, he could aim his serves in different ways to avoid the opponent, do underhand serves, his skills could probably control the ball in other ways. THis may suggest that he hits the ball at an opponent who cant return to make them look dumb purposefully. This ensures sanada is treated with the same respect by subjecting sanada to the same process other opponents yukimura plays.
I can only state echizen's match with him as a reference, where the ball ends up hitting echizen, usually while the opponent is standing most still. Also sanada's clothing is shown as dirty at the end of the match with yukimura, since sanada didnt give up (by lying down on the ground forfeiting the match in mental anguish) and the end score shows so. also we see that a ball gets hit at sanada. (note: manga may be boring if same pictures are drawn ie being hit with the ball, so 1 picture could makes it point and doesn't have to be redrawn)
again i stress yukimura can aim the ball anyway he likes due to his skill level to avoid hitting the opponent after the a ball bounces, but he chooses not to.