I get curve balls one of two ways. When the pokemon is "near", I spin the ball and throw so that loops around and hits the mon on the opposite side from where I threw. For "far" pokemon e.g. zoobat, I spin the ball and throw a little to the upper left of where I want to hit. The spin will arc the ball into the pokemon. My success rate at these two methods is not perfect, but much better than random.
GamePress
Curveballs - how do they work?
Anyone have a video of how Curveballs work after Gen2?
I seem to get them fairly randomly, by accident. I've tried a few things that don't work:
Spinning the ball appears to have no effect. Makes a nice graphic, but if I take a straight shot with a spun ball, it isn't a curveball.
My curveballs tend to be when I make a bad shot (too far to left or right), but still hit. I tried shooting from the lower-left corner of the screen instead of the lower-center, but that didn't work either.