Sprinters start their races from a crouched position with their bodies well forward of their feet. This position allows them to accelerate quickly without tipping over backward. Explain.

We can explain it in term of center of mass and torque. When the sprinters start their race then the ground exerts the force towards the center of mass and thats how the torque can be prevented from acting on the sprinter. In this way the crouched position allows them to accelerate quickly without tipping over backward.