Which direction is my player facing?

I am creating a simple top-down 3D game where two players run around kicking a soccer ball. I have colliders on the players and the ball, and wrote a simple script to have the players kick the ball whenever they come in contact with it. HOWEVER, I can’t figure out which direction a player is facing when she contacts the ball, and thus which direction the ball should travel. In the following code I used a Vector3.left so that the ball did SOMETHING, but obviously I can’t have a game where everyone kicks the ball left.

How can I tell Which direction is my player facing when she contacts the ball (as in, what can I replace “Vector3.left” in my code with?)

NOTE: Code is attached to each PLAYER, “other game object” is the ball<<

using UnityEngine;
using System.Collections;

public class ShootBall3: MonoBehaviour {

void OnTriggerEnter(Collider other) 
{
	//facing = Vector3.forward;
	if (other.gameObject.tag == "Ball") {
		other.rigidbody.AddExplosionForce(2000f, Vector3.left, 2000);
	}								     
}

}

other.rigidbody.AddExplosionForce(2000f, this.transform.forward, 2000);

Vector.up, Vector.right, Vector.forward (etc) are all world-space. So they will always go up, right, forward (etc) in relation to world point (0,0,0).

transform.up, transform.right, and transform.forward are all local-space. So they will go up, right, and forward in relation to the object they are attached to.