In American football, a turnover on downs occurs when a team fails to convert a fourth down into a first down by gaining the required yardage.
A team has four chances (each chance is called a "down") to gain ten yards or to score. Any ground gained during one down short of these ten yards is kept for the next chance. Thus, if a team gains four yards on first down, it then has three chances to gain the six remaining yards. If a team gains the required ten yards, it receives another four downs to gain another ten yards (an event called a "first down") or cross the goal line for a score.
Though teams have four chances, in most cases, only three are used. Usually, if a team fails to gain the needed yardage after the third down, it will then punt the ball, offering the opposing team possession, or attempt to kick a field goal if close enough. The opposing team will start their new set of downs to wherever the punt returner can advance the ball prior to being tackled, or where the punt comes to rest, after rolling to a stop.
But in some instances, a team may elect to use its fourth down to try to gain the yardage, rather than punt. This is often referred to as "going for it" or "sticking" (as opposed to "kicking"). Factors that may lead to a team making this choice are:
"Going for it" has a disadvantage in that if the fourth-down conversion attempt fails, the opposing team will immediately take possession of the ball, thus causing a turnover on downs.