I don't really recall when I first came across this type of feeding.
Have been working with another coach, a former D2 player, on his serves & returns. I had asked them when he first saw this type of feed. He had indicated that he recalls seeing it about the same time that he was learning about the Spanish method of teaching.
Not sure if this is part of that system since the Spanish system employs quite a lot of hand-feeding drills. I first learned of the Spanish system around 2011.
From TennisPlayer.net:
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