Instead of disabling the whole body, just disable the neck and spine motors. The arms and legs keep animating, but the upper body flops back when hit.
If you meant something else, please provide more details (e.g., "I need a research paper on ragdoll physics engines" or "I need the full Ragdoll Engine script from a specific Roblox game"). I'm happy to help once the request is clear. Ragdoll Engine Script
Open Roblox Studio tonight and paste your first Ragdoll Engine Script. Your players will thank you for the laughs. Instead of disabling the whole body, just disable