At rest the player exerts force (weight) on the ground. When the player begins to jump or pivot, they have to pull their feet upward to either move them, or low

At rest the player exerts force (weight) on the ground. When the player begins to jump or pivot, they have to pull their feet upward to either move them, or lower their center of gravity. This can be measured as a decrease in weight (force) exerted on the ground.