Concussions are no joke. They seem to happen more frequently with each passing year, and the NFL gets less careless with how they handle them with each passing year, as well.
Still, that doesn't stop them, and even when teams are careful, a second concussion can happen easily, and knock a player out for a lengthy period of time.
According to Hagen-Law.com, there were roughly 162 "head injuries" in the NFL in 2011, with just under 11 concussions treated on average per week (here's a deeper look at 2010's concussions).
In all, Hagen-Law suggests the math equates to there being a 72% chance that there will be a concussion sustained by a player in every NFL game. Those aren't odds to take lightly.
With that said, here are a few big names that are at risk of missing action if they take another hit to the head in 2012:
Kevin Kolb, QB, Arizona Cardinals
Kolb didn't just have a bum foot in 2011 - he also dealt with a concussion. In fact, Kolb later said that he still has "concussion symptoms" for "weeks" after the season was over.

Considering he plays a position that takes a ton of hits and he's already succumbed to a head injury, this doesn't bode well for him going forward. As if he didn't have red flags already with his erratic play and foot, now Cardinals' fans have to wonder if he'll get up the next time he gets hit in the helmet.
Jahvid Best, RB, Detroit Lions
Best hasn't made it through a full 16 games since entering the league two years ago. He dealt with a nagging foot injury in his rookie year and missed a game, and then succumbed to a dangerous concussion that forced him to miss the final 10 games. And he's still not fully recovered.

Rumors have been swirling all off-season that Best might even consider retiring at just 23 years old due to concussion symptoms and fear of immediate re-injury. As it stands, the versatile and explosive running back is training hard and looking to come back at full health in 2012. But to say he's in danger of going down with the first big hit is a vast understatement.
Austin Collie, WR, Indianapolis Colts
Collie found a way to stay healthy in 2011, and a lot of that probably had to do with the Colts' quarterback's inability to get him the ball at a consistent rate. However, coming out of 2010, his career appeared to be in jeopardy due to several concussions.

Collie claimed he never thought about hanging up the cleats a year ago, but another concussion may force him to rethink things - especially given the rise of concern over concussions in recent weeks. Collie is still a very effective slot receiver, but it's his role and willingness to sacrifice his body over the middle of the field that is discouraging. If he's healthy, he could develop into one of the game's best possession receivers. However, Colts' fans may have to cross their fingers for that to happen.
Ultimately, every single NFL player is at risk of suffering a concussion at any time in any game. There's no great way to predict it or prevent it. Teams and players can only recognize it's happened, and treat it after the fact. However, the three guys above have had one or more concussions in their recent past, and should be closely monitored going forward.
Did we miss a big name that has had too many concussions to count and is a risk to go down at any time? Comment below!