3. Marion Barber
We all remember the "Marion Barber Game," right? The Bears held a 3-point lead on the Denver Broncos, led by Tim Tebow, and could ice the game late in the fourth quarter. All they had to do was run out the clock, which is precisely what they attempted to do.
Barber took a handoff, and instead of going down inbounds, he ran out of bounds, stopping the clock. What ensued was pure, unadulterated nightmares for Bears fans, and for the rest of their lives. The Broncos would get the ball back, kick a lengthy game-tying field goal to take it into overtime and, that's not all.
In overtime, Barber would fumble. The Broncos went on to win the game, and at that point, Chicago was fighting for their playoff lives. That loss would look darn close to the final nail in their coffin. Barber played just that 2011 season for the Bears, rushing 114 times for 422 yards and six scores, and that one costly fumble.
His best days were behind him, which came in Dallas, where he rushed for over 4,300 yards and 47 touchdowns in six seasons, earning one Pro Bowl bid.