initial velocity for instantiated ragdoll prefab

Im instantiating a ragdoll prefab and I need it to have an initial velocity. I keep getting hit with null reference exceptions.

(the object is destroyed when the space bar is pressed)

public Rigidbody rag;

void OnDestroy()
{

rag = Instantiate(ragdoll, transform.position,transform.rotation) as Rigidbody;
rag.AddForce(100,100,100);//null reference at this line
}

Are you instantiating an entire ragdoll prefab? If so, it’s unlikely to have just a single rigidbody which controls the entire ragdoll. Try doing something like this, instead (without the public rigidbody, at the top)-

void OnDestroy()
{
    Vector3 startingVelocity = rigidbody.velocity;
    // Assuming you have a rigidbody on your character, otherwise work this out some other way

    GameObject rag = Instantiate(ragdoll, transform.position, transform.rotation) as GameObject;
    foreach(Rigidbody body in rag.GetComponentsInChildren<Rigidbody>())
    {
        body.velocity = startingVelocity;
    }
}