I am so F'ing mad that Speedball doesn't give you a warning when you target it
Yes, I realize that I'm an idiot and after a decade of magic I should know that reading the card explains what the card does. HOWEVER, this might just be my declining mental ability, but I'd argue that the rules text is deceptively difficult to parse and the plain english of it implies that it's the controller of the spell who retargets, not the speedball owner. But Arena is generally extremely generous about warning you when you might be doing something with consequences you're not picking up on, and the stupid thing has hexproof+, I can't think of a single scenario where targeting an opponent's speedball is something you should do, I would argue that this card is the single most obvious scenario for Arena to ask if you're really sure you want to do that.