Just assume the other jersey is the chase figure and that's the reg. 98% of sportspicks have a chase figure and the easiest way is to look at the back of the packaging. If the jersey on the figure in your hand is the same as that pictured on the back, it's the regular, not chase figure.
That said, there have been some notorious examples of McFarlane messing with people's minds or outright screwing up. Thornton 1 is a good example. The packaging set up had the regular appearing to be the chase. Kind of funny really. Let's put it this way, if it's two in the afternoon and you find a Thornton, it's the reg.