I know someone who got into boxing because of watching ROCKY 1. That might do it, if you pick the potential future boxing fan carefully.
My knowledge of fighting doesn't span as far back as some of you, but I'd show them something with drama early on to catch their attention like pacquiao marquez 1 or trinidad vargas.
Hagler-Hearns baby. Hagler-Hearns. Chavez-Taylor McCallum-Toney Tyson-Holmes So many more, but we'll keep it short.