One Rigify leg deforms differently?

First confirm which Rigify rig deforms the mesh

The metarig is a placement template. Rigify generates a separate control rig, and that generated rig drives the mesh through its deform bones—usually the bones whose names begin with DEF-.

1. Select the mesh and inspect its Armature modifier

   The Object field should point to the generated rig you intend to pose, not an old generated rig, duplicate armature, or the metarig. Confirm that the modifier is enabled and that Vertex Groups are active.

2. Pose the generated rig's controls

   Move the same control on each side through the same angle. If the controls differ before the mesh moves, compare the metarig placement and regenerate on a copy rather than repainting the mesh.

3. Verify the deform chain underneath

   Check that the expected DEF-thigh, DEF-shin, and neighboring deform bones exist on both sides, have Deform enabled, and follow their controls symmetrically.

Compare one stretched vertex, not the whole heatmap

Weight Paint colors are useful, but blue can hide a tiny nonzero influence and the active group may not be the group causing the pull. Preserve the failing pose, enable the Armature modifier's Edit Mode display, then inspect one visibly stretched vertex.

1. Read the numeric weights on the bad side

   In Edit Mode, select the vertex and open the 3D Viewport Sidebar's Vertex Weights panel. Note every deform group and value, especially a shin, foot, pelvis, or opposite-side group that should not affect the upper leg.

2. Compare the corresponding vertex on the good side

   Use the mirrored side as the reference. Compare the matching .R and .L DEF groups rather than assuming Automatic Weights produced identical assignments.

3. Remove only the proven stray influence

   On a saved copy, remove the bad vertex from the unrelated group or correct that one value. Lock groups that are already correct, normalize the affected deform groups, and retest the same pose.

If the weights match, compare the rest setup

When corresponding vertices have matching weights but only one side collapses, the cause is upstream of weight painting. Compare these side by side:

• Bone placement and roll: the joint centers and local axes should mirror, not merely look close from one view.
• Generated constraints: confirm both control chains drive the matching DEF bones and use equivalent limits.
• Object transforms: the mesh and intended armature should not carry an unexpected asymmetric scale or rotation. Apply transforms only with a saved copy and a clear understanding of the already-bound setup.
• Modifier stack: compare Mirror, Corrective Smooth, Subdivision, and Armature order. Temporarily disabling one modifier on a copy can reveal where the asymmetry enters.

Once the first mismatch is found, repair that link and test a short range of hip and knee poses. One good screenshot is not enough to prove the joint holds through motion.

Use the analyzer for weight relationships

The free SkinSmart beta can flag suspicious armature-weight relationships and select affected vertices after the correct rig and modifier path are confirmed. It does not rebuild Rigify controller logic, alter the mesh, or guarantee that an arbitrary production rig can be repaired.

References

• Blender Artists: one Rigify leg deforming differently, the public symptom that prompted this guide.
• Rigify basics: the metarig-to-generated-rig workflow.
• Armature Modifier: verify the rig target and vertex-group deformation path.
• Vertex Weights: inspect exact groups and values on a selected vertex.