between positions to increase the speed of play; one official will approach the bench whilst another, usually the closest to the bench at that time, will move to occupy his position. This also prevents one official from always working one particular team's basket throughout the course of the game. In "three-person" mechanics, the court is further divided among three officials, with the lead (baseline) official determining the position of the other two officials. Normally, the lead official will move to the side of the court in which the ball is located (strong side), particularly if there is a "post-up" player in that position. The official that is on the same sideline as the lead official then takes up a position approximately level with the top of the three-point line and becomes the "trail" official, while the third official will stand across the court near the free-throw line in what is called the center position. This creates a triangle coverage of the court. Often, the lead will switch sides of the baseline during a play, requiring the trail to move down to be level with the free-throw line and become the new center, while the center will move up and become the trail. As the ball moves to the other end of the court in transition, the lead will become the trail, the trail will become the lead, and the center official will remain in the center (unless the new "lead" moves across the baseline to cover the strong side, in which case the center official and trail would then switch positions.) Difficulty Basketball is regarded by many fans as among the most difficult sports to officiate. Usually basketball officials have only split seconds to determine if an infraction has occurred, due to the speed of play of the game and the officials' proximity to the action. Especially difficult are the "charge/block" call and shooting foul/block attempt. Officials often rely on instant replay to review plays. Only recently has a coach been allowed to contest a call by the official, or one missed by them, but this is only valid for a specific window. Despite the misconception that basketball is a non-contact sport, officials often let a large amount of marginal or incidental contact pass uncalled. An official must always be aware of not just what is happening around the ball, but the roughness of play going on around the whole