Football's Brutality
Football was known as a violent game from the start. See this from The Boston Globe on Christmas Day in 1881:
As I mentioned yesterday, the problem with the game at this phase of its development was that it was little more than two sides grabbing the ball and trying to run it straight at the defenders. Not only was blocking not allowed, but it was impossible, since any offensive player in front of the ball was deemed offside. It was like a game of rugby, but one in which all the hitting and pushing was directed only at the ball carrier.
As this article clearly states, the problem with the game had nothing to do with the number of players on the field, and had everything to do with the restrictiveness of the rules at the time.
The lack of blocking and the rough-and-tumble nature of the game is also the reason why there were so many safeties in those days. It was extremely difficult to move the ball forward, and the prevailing strategy of the time was to either punt the ball as far down the field as possible or to simply take a safety to get the resulting free kick.
I’m not entirely sure what the “block game” that Princeton used is referring to. That’s going to require some more research. Let me know below if you know what is going on.