Making an Object Move opposite to a FPS Camera, Please


I am using a mouse driven camera and this is the code :

void Camera::updateCameraVectors(void)
// Calculate the new Front vector
glm::vec3 front;
front.x = cos(glm::radians(this->yaw)) * cos(glm::radians(this->pitch));
front.y = sin(glm::radians(this->pitch));
front.z = sin(glm::radians(this->yaw)) * cos(glm::radians(this->pitch));

glm::vec3 temp = this->front;
this->front = glm::normalize(front);

// Also re-calculate the Right and Up vector
this->right = glm::normalize(glm::cross(this->front, this->worldUp));  // Normalize the vectors, because their length gets closer to 0 the more you look up or down which results in slower movement.
this->up = glm::normalize(glm::cross(this->right, this->front));

**// this is my idea that is not working**	
 ball.xadj = ball.xadj - front.x;


I just need the right quantity to translate an object that is opposite this camera’s movement. How can I get these amounts? I thought it was the front variable but this didn’t work right.

Thanks in Advance,

Edit: Basically the ball should stay on the center of the screen.