Originally Posted by toly
Ball rotation about vertical axis is sidespin. It is common practice to define direction of the sidespin from above or below view.
That may be common for when you deal with sidespin as the primary rotation,
But we are not talking about a pure type sidespin, but more of a side aspect to
something like the canted axis for the earth.
I specified several times from the hitter's perspective.
Maybe to make it simple for you, we can address it as which way it will curve;
tail off to left or right.
Nadal's lefty I/O Fh will tend to tail off to the left.
Fed's righty I/O Fh will tend to tail off to the right.
Does that make sense to you?