In soccer, tackles are done with the feet around or against the opponent's feet. To be legal the opponent must have control of the ball at the time. Since soccer is a high-speed game, various rules protect the player running with the ball. However, from 2017, tackles from any direction that endanger an opponent's safety may result in the offender being sent-off. This includes "scissoring" which is likely to be punished with a send-off (red card), as it poses a high risk of severe knee injury to the player being tackled. A "studs up" tackle may be dangerous. Referees may caution (yellow card) players who commit such challenges. 