I'll tell you something, i use, like him, an eastern grip, it's true that some times, well actually many times, i find myself hitting with an eastern to a semi-western grip, and that's completely normal during a rally, because my hand slips from an eastern to a kinda semi-western, so i guess that's what happens to him as well, that's why, if you surf the net, you will find videos, pictures showing eastern and semi-wersten grips. It's not something static, at least for me.
That's why if you ask me which is my grip, i will tell you eastern...but that's not really true....
That doesn't happen vice versa btw, somebody using a western, or a semi western grip will never end hitting with an eastern at the end of a rally.
Don't know if you play tennis and which grip you use but check next time you play, you'll notice this
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