Initially, football (college ball, intramural games) of the 1800s were always played on Fridays and Saturdays, but as the professional sport was introduced in the late 19th century, Sunday's - church days -- became game days so that more fans could be brought to the stadiums.
At the time area around the designated ball fields could only seat under 100 people, and -- compared to today -- looked more like a giant backyard than a playing field.
Not widely accepted at first, many cities banned any games from being played on Sunday. Only over time did the first day of the calendar week come to be accepted. Once the professional game gained popularity --after 3 decades of play from the Ohio League to the NFL of the late 1940s-- was Sunday football the cultural norm.
Teams could get in serious trouble from city councils, if games were played on Sunday's where fines could even be levied. Never mind that most people of the day were adverse to even attending a sporting event on "the day of rest." Although, everyone knows that if work had to be done on the farm, nobody was sitting around doing nothing -- it still wasn't widely accepted. But then that was well over a hundred years ago. Now there's not a day people don't work or play.