Charles was going out of bounds and collided with the Lions' mascot, but appeared to have injured himself before the collision. Charles went down immediately clutching his left leg, and after he couldn't stand on his own, the Chiefs brought out the cart. No further information is available as to the seriousness of this leg injury, but if you're a Chiefs fan, this is already pretty serious.
After Charles, the Chiefs have a combination of Thomas Jones and Dexter McCluster to fill in the running back position, but the two combined don't equal the talent and production that JC Superstar brings to the table. Fantasy owners will want to jump on Jones, as he'll get the bulk of the looks near the goal line, in case this injury is of the multi-week variety.
Chiefs fans are pretty devastated. See SB Nation's Chiefs blog Arrowhead Pride if you're into some good, ol'-fashioned schadenfreude.