Why do people have such a hard time with what "luck" is? Any forced turnover is not luck.
For instance, and the best case of what's luck and what's not all in one little play. When ATL played SF and Clements tried to run the ball back instead of knowing the situation and going down, the fact that he didn't have the smarts to go down was lucky for the Falcons, but White running down the play and stripping the ball to get it bak for the Birds was not luck.
It's really not that hard.