Collapsing the Back Side
Also known as: back knee collapse, sitting down on the swing
Collapsing the back side is when the back knee and hip drop and cave in instead of staying stacked. It drains power and lowers the swing plane unpredictably.
A stable back side acts as the post the swing rotates around. As the hips turn, the back knee should stay generally over the back foot. It should not drop down and cave inward toward the front leg. When the back side collapses, the whole body drops in height during the swing. That both loses rotational energy and changes the bat's angle of approach in a way that varies from swing to swing.
Example
The back knee caves inward and drops during the swing instead of staying firm and rotating. The hitter's bat path becomes steeper and less consistent than intended.
How it shows up on video
A collapsing back side shows the back knee dropping in height and rolling inward toward the front leg during the swing, rather than staying at a consistent height and rotating around a stable base.
Common mistakes
- Trying to generate power by sitting down into the swing rather than rotating around a firm back leg
- Weak or fatigued lower-body strength allowing the back knee to cave under rotational load
- Overstriding, which puts the back leg in a weaker position to resist collapse during rotation
In SwingVantage Motion Lab
Motion Lab reads your back knee's height and position from pose through the swing, which shows whether it drops and rolls inward.
Related terms
- Back-Side MechanicsBack-side mechanics are how the trail hip, knee, and foot fire in the swing. This "engine" side drives rotational power from the ground up through the barrel.
- Hip RotationHip rotation is the turning of the hips toward the pitcher during the swing — the single biggest source of rotational power in a slow-pitch hitter.
- Rotational PowerRotational power is the energy generated by rotating the hips and torso into the swing, transferring ground-force and core energy through the arms and into the barrel.
- Hitting Off the Back FootHitting off the back foot means the weight stays planted on the back leg through contact. That makes an arm-only swing with little rotational power.
- Weight ShiftWeight shift is the deliberate transfer of body weight from the back foot during the load to the front foot during the swing, generating forward momentum that adds power at contact.
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