This is the most thorough review of the evolution of football rules that I have encountered. My favorite part of the book concerned the 1900-1915 era when there were dramatic changes to the rules to reduce the number of deaths and injuries that occurred in football. Some of the ideas discussed for rule changes seem whacky and a few of those changes were implemented and later dropped.
My primary takeaway is that some rule makers opposed changes to the game, while others saw the need to change fundamental elements of the game to allow it to survive. There are lessons there for anyone thinking about rule changes that will be needed to reduce concussions and CTE arising from the game as it is played today.
If you're interested in the long history of how the rules of football have evolved since the genesis of the game - with lots of historical context thrown in - this is an interesting read. It can be dry at times but there's not shortage of "Wow! Who knew?" moments.