Sprint-toggling, also called the “running trick”, is a distraction technique which uses the noise made by sprinting to distract a guard or multiple guards, before disabling “sprint” to move away from the interest point safely.
Sprint-toggling is a powerful and versatile way to manipulate guards, which can be used in many situations to avoid knocking out a guard who otherwise blocks the way. Sprint-toggling can also be used to make a guard open a door to activate a Shock Trap, to bring multiple guards together so they are within the area-of-effect of a Flash Grenade or similar, or to control a guard so you know what they will do without observing their movement for 1 AP. Additionally, sprint-toggling gives information about nearby guards, though usually you do not want a sprint-toggle to be heard by a guard you didn't already know about.
Sprint-toggling takes advantage of the “sprint” ability's mechanic which allows the agent to stop sprinting if they still have at least their base AP; typically this means an agent can stop sprinting after using 3 AP, or after using 4 AP if the agent has Speed 5. Being encumbered usually prevents an agent from sprinting, so it is advisable to drop excess items at the end of your turn if you might want to sprint-toggle the next turn, and then pick them up again once you begin sprinting. It is also often worth activating “sprint” before peeking or observing a guard's movement at the start of your turn, if you might want to do a sprint-toggle afterwards.
Sprint-toggling is one of the most important techniques to learn if you want to beat the game at Expert Plus or higher difficulty settings, and is practically essential for the No Items and Pacifist challenges.