We're conditioned to think of a gain of just two or three yards as, well, a gain. But unless those couple yards are for a first down, it's anything but a gain. About 60 percent of all running plays are setbacks, meaning that the offense is less likely to score after the play than it was before. Offenses might as well be throwing downs away. Defenses would be happy to spot an offense a third-and-four every time—the conversion rate on third-and-four (55 percent) is lower than for a series that starts with a first-and-10 (67 percent).
You can read the post at either site: Slate or Deadspin.