From the standpoint of most spectators, football is all about the game. From the standpoint of most players, football is all about practice. What players go through at practice, particularly two-a-days, can be more grueling than what they go through during games. When coaches tell players, "Compared to practice, the game will be fun," they aren't kidding.
Though spectators and viewers think of games as the dangerous part of football, because it's during games that injuries are widely seen -- coaches whom I have interviewed think players are more likely to be injured at a practice than during a game. Partly this is simply because players spend so much more time practicing than performing, meaning more hours of risk.
But there's another, darker reason: Games are observed by the public and supervised by officials. At practice, there are no rules. Some coaches are conscientious about practice safety. Others are not. The Oklahoma Drill -- two players confined to a small area, instructed to run and smash into each other repeatedly until one yields -- probably has caused more injuries than the kickoff returns the NFL is concerned about. The Nutcracker Drill -- a version of the Oklahoma, in which two players repeatedly bash helmet-to-helmet -- not only is sadistic, it is all but designed to cause concussions and head and neck injuries.