Ah, my biggest grip about football. Baseball gets all the blame for being slow, but football and basketball, relative to their "periods" if you will, take longer.
That's pretty much completely false. According to the American Journal of Sports Science, in examining the features of successful football players, starting at the high school level and then moving up to college and into the pros, football players with higher level of body fat tend to get injured less from football contact (about 25% less) than those who had leaner body fat percentages. Fat isn't designed to serve as padding for the body, but by virtue of the fact that it puts greater space between the impact and the functional parts of the body, it is. Obviously having less body fat may be correlated to an athlete being more lissom than a heavier athlete, however it does not correlate to being able to take hits any better. Muscle being "hard" is irrelevant, especially since muscles are only "hard" if they are stimulated often. In addition, when muscles are put under stress, they tend to put additional stress on tendons, bones, and ligaments, while fat tends to be more superficial to the skin that muscle, thus preventing impacts from being as harsh.