Channel 4's NFL coverage started in 1982, just before my 13th birthday.
I was already following the sport* because my dad had previously gone to Buffalo Bills games when working in Rochester NY, and began working at the Xerox office in El Segundo just as the Raiders moved their training camp nearby
He bought me a t-shirt that said on the front......
OaklandLos AngelesEl Segundo
RAIDERS
On the back it said...."Where the hell is El Segundo?"
I don't think that it was official merch

By 1983 I was walking the mean-streets of the Forest of Dean wearing a Marcus Allen jersey
(* via American Forces short-wave radio)