Hi again Erik, and thanks for your detailed reply.
The ball shows as a 10x10 circle blob in the grayscale 1024x768 image. It is in bright color while background is darker. Something like about 80 to 100 less for color value. The guide how to implement is interesting. I am afraid that it looks beyond my expertise to implement a hough transform though. I would have to find someone else to help me out on that.
However the other option of training a custom NN to look for the blob can be interesting. The only reason I have avoided that has been that I was worried that the NN based blob detection may not provide a precise boundingbox. My aim is to know if the ball is moving or not, so it is essential to get as good of a bounding box as possible that repeats frame after frame. What is your expectation on the results of an own NN plus Harris corner detection (wonder if it works on circles?).