Annotating sports video: design principles?
I'd think the best principal would be to ensure that motion always trump graphics.  Ie, any pixels that are detected as having velocity that is not equal to the velocity of the background should be rendered over the graphics.  This might be difficult to accomplish without purpose built software, but such an approach should keep the graphics from going over any action.  You actually already see this with things like American "Football" (not soccer) games where they render on lines for things like line of scrimmage and first down.  The perspective makes it look like it is simply graphics on the field even though they are actually added electronically.