Football 2 (or II) was released in 1978. It is the Sequel to the popular Football I game. It adds the functionality of running forward and backward, passing, etc (and actually has a 10 yard playing field, not 9 like Football I). This game also has an 'Easter Egg' of sorts, if you hold down the 'Pass' button while turning on the game, you effectively get Pro 3 or Pro 4 difficulty settings for the game play (i.e., if you have the switch on Pro 1, holding down the pass will give you Pro 3, etc. Pro 4 is VERY fast and difficult to play.)
Football was released in 1977. It was labelled either Football or Football I (after the release of Football II). Early models of Football had an AC Adapter jack which was removed on later models (which would only run on batteries).
First released in June of 1977 as the second game released by Mattel (Auto Race was the first) and sold through Sears. After less than 100,000 were made, Sears (using a computer model based on initial sales figures) determined that the games would not be big sellers, and most of the production for Football and Auto Race was stopped. Within 6 months, it became obvious to Sears that their prediction was wrong, and production was started up again and reached previously unknown levels! (Reaching as many as 500,000 units a week by mid-February, 1978).