I played football all through high school and then 3 years of college (Div.III). I was a 5'9", 185 corner, that, on a regular basis, got his brains knocked out. Not only by 300lb. pulling guards and fullbacks that weighed in at 250, but by halfbacks and tight ends that weighed just as much as I did.
I did it because I loved the game, not because I had any shots at getting paid for it.
These guys that are playing in the MFL (the Mutha....errr...wait...NFL), are the biggest, fastest, and hardest hitting guys in just about any sport. Yea, we got big guys in hockey and rugby and Aussie rules football, etc., but for the most part, these guys are just plain BIG.
Despite that size and strength, there's still a limit to what any human being can take. These guys make the conscience decision to go and play pro ball. With the big-dollar contracts comes the risk of getting hurt, sometimes seriously. Pay me the league minimum for a rookie ($310K for 2010) and I'll go out there and hit anything that moves. That's 6 years' worth of my regular pay.
I look at these huge contracts, I look at ticket prices, and I understand that its just a business. Players, for the most part, are idiots. If you made tens of millions of dollars over a 5-10 year pro football career, would you be smart and prepare knowing that you've got a career expectancy of less than 10 years? Would you invest? Or would you buy a huge house and dozens of cars, knowing full well that after you retire (or have a career-ending injury) that you won't be able to sustain it?
Concussions, head-hunting, and cheap hits are always going to be a part of the game. In some instances, its deliberate, in others, it happens simply because of the way two players come together. This is where instant replay should play a bigger role, in determining the circumstances of the hit. The game has slowed down enough now (along with network replays and TV timeouts) that there's no reason for the upstairs official to look at a play and determine if it was intentional or accidental.
I watched a game last week, a lineman came through the line, was held, spun around (he had his back to the QB at this point), and was blocked into the QB. The lineman's hand hit the QB on the helmet, bang, 15-yard penalty. The lineman never even knew he hit the QB's helmet (who lowered his head and moved to the side to avoid the contact). This is perfect example of how the rules have gotten out of hand (no pun intended).
Personally, I think cops and combat soldiers deserve to be paid the highest salaries.
J