Introduced in The Amazing Race 12, the U-Turn is an obstacle that teams can use to slow down a team behind them. After completing a chosen Detour option, a team will come across the U-Turn board and may use the U-Turn to force another team to also complete the other Detour option they did not originally choose. The U-Turn generally appears after the Detour, although one in The Amazing Race 27 appeared before the Detour.
Originally, the U-Turning team would have to place a small sticker with their own picture on the board as well, identifying themselves as the perpetrators. Teams are given these "Courtesy of" stickers at the beginning of the race. If they lose these stickers, they will not be able to use the U-Turn. However, more recent seasons have utilized an electronic U-Turn board with touch screens, eliminating the need for the stickers.
Teams are not aware of which teams are ahead of and behind them upon arrival at the U-Turn. As such, it is possible that a team may attempt to U-Turn someone that is ahead of them. In this case, the U-Turn will be ineffective. This has happened numerous times.
A team can only use the U-Turn once during the race (as represented by the single "Courtesy of" sticker they receive). However, a team can be U-Turned any number of times. Additionally, a team is still free to use the Yield after using the U-Turn. This rule is still in place, despite the move to touch-screen interfaces and the elimination of the stickers. This rule is not used in The Amazing Race Canada, and was not enforced during The Amazing Race 29.
A team that does not complete their second Detour after being U-Turned may receive a smaller penalty than the usual 6-hour penalty for not completing a Detour (depending on the version of the show)
In a Blind U-Turn, the U-Turning team will not have to use their "Courtesy of" sticker to identify themselves as having used the U-Turn, thus remaining anonymous. As such, they will still be able to use a regular U-Turn, should one appear later in the race (as they still have their sticker).
In the Australian version, this is known as an Anonymous U-Turn.
More recently, the U-Turn has evolved into the Double U-Turn. All American seasons use this variation exclusively, as do many international versions. In this case, two teams may use the U-Turn on two other teams. If a team arrives and discovers they've been U-Turned, they are free to U-Turn someone else before completing their second Detour (provided the second U-Turn is still unused).
Blind Double U-Turn
Recent versions of the American show have combined the above two twists into the Blind Double U-Turn, where both perpetrators will remain anonymous. This is usually paired with a non-blind U-Turn later in the race.
Some versions of the show feature a starting line task, and the last person to complete these tasks will be automatically U-Turned on the first Detour of the race.
Some international versions have introduced a more unique version of the U-Turn, wherein each team must vote for a U-Turn target at the beginning of the leg. The team that receives the most votes will be U-Turned after the leg's Detour. This is sometimes known as a Must-Vote U-Turn.
In two legs of HaMerotz LaMillion 3, this was combined with the Double U-Turn. In this case, the target that received the most votes (and only this team) could then choose to use a second U-Turn on another team.