someone earlier said, that English never reverses....I disagree with that statement...I may be wrong, Im not sure.
That would have been me. For this discussion, I am referring to the cue ball ONLY. Let's say you put left on the cue ball. If you look straight down from above, that would be clockwise. Now if the cue ball contacts another ball or a rail, hence changes direction, the spin on the cue ball is still going to be clockwise. The rotation of the earth doesn't just stop and turn around and go in the other direction.
Now this clockwise spin is the same thing as saying left spin no matter what angle you are looking at it from. If you go around to the other side of the table and look from the north, or look from the south, east, west it will always be left and when looking from above it will always be clockwise.
Now when answering the OP's question, I was saying it is important to visualize the cue ball as it approaches the rail in order to know what effect that spin is going to have coming off the rail. In determining that, you have to judge it in the context of the cue ball moving in the forward direction (noting that linear direction is a different thing than spin direction).
And to address another thing too, I also notice a lot of people using the term English wrongly. English is left and right spin. Top and bottom spin is not supposed to be called English. But hey, what are you going to do.
Here is an entertaining shot on diamond tables. Fairly tight angle bank into side pocket. Bank ball long with inside English. Hits 4" past side pocket, and then reverses cross side into other side pocket. With inside English, this shot should go farther away from second side pocket, not reverse right back into it. (if I don't hit this shot hard enough ive actually had it reverse several inches past second side pocket).
Unless Im really misunderstanding something here, that inside English I have on that bank, HAS to reverse for that bank to come back like that.
If anyone could explain this one to me, Id appreciate it, because this one I cant figure out on my own.
Now, in this case, you are involving another ball. The spin of the cue ball is not changing. But some of the energy from the spin from the cue ball is transfered, in some form, to the object ball, causing it to spin (or appear to spin?) in the opposite direction. That may be an over-simplification, but makes my point. Also, if you are hitting it hard, that shortens the angle of bounce off the rail, and exaggerates the overall effect of the direction change of the object ball off that rail. Great shot to know.
Fatz