Context: The NFL was the first league ever to use the wild-card format. The decision to implement a Wild Card coincided with the completion of the AFL-NFL merger in 1970. Prior to the merger, the right to compete in the postseason for the NFL title was restricted to division / conference champions. Until 1967, a tiebreaker game was played to resolve a deadlock for first place in either of the two conferences. When the league expanded to 16 teams, it realigned into four divisions and expanded the playoffs to two rounds. Tiebreaker games were eliminated in favor of the use of performance-based criteria to determine division champions. The rival American Football League, which reached a final size of ten teams in two divisions, also restricted its postseason to division winners until the 1969 season (the AFL's last as a separate league) when it expanded the playoffs to include division runners-up. The runners-up played the winners of the opposite divisions for the right to contest the AFL Championship Game.

Question: when did the wild card start in football?
Steam of consciousness below:
To answer this question, we should know that: The decision to implement a Wild Card coincided with the completion of the AFL-NFL merger in 1970.
So, the answer is 1970.