Attack animation Wont Play

My zombie attack animation “swing” wont play, it will play if animation “walk” isn’t in the script but other than that it wont play.
Please help me.

My Script

using UnityEngine;
using System.Collections;

public class AISimple : MonoBehaviour {
	
	public float Distance;
	public Transform Target;
	public float lookAtDistance= 50.0f;
	public float chaseRange= 20.0f;
	public float attackRange= 5.0f;
	public float moveSpeed= 1.0f;
	public float Damping= 6.0f;
	public float fov= 160.0f;
	
	private RaycastHit hit;

	public CharacterController controller;
	public float gravity = 20.0f;
	private Vector3 moveDirection = Vector3.zero;


	bool LineOfSight ( Transform target  ){
		if (Vector3.Angle(target.position - transform.position, transform.forward) <= fov &&
		    Physics.Linecast(transform.position, target.position, out hit) &&
		    hit.collider.transform == target) {
			return true;
		}
		return false;
	}
	
	
	/*
  This ai will fly and move through objects inlcuding terrain!
*/
	void  Update (){
		
		if (LineOfSight(Target) == true && hit.transform == Target) // Target is player
		{
			
			//enemy sees you - perform some action
			
			// Gauge the distance to the player. Line in 3d space. Draws a line from source to Target.
			Distance = Vector3.Distance(Target.position, transform.position);
			
			// Turn yellow enemy is getting close. Will chase soon.
			if (Distance < lookAtDistance)
			{
				
				lookAt();
			}
			if (Distance < attackRange)
			{
				
				attack();
				animation.Play ("swing");
			}
			// Attack! Chase the player until/if player leaves attack range.
			if (Distance < chaseRange)
			{
				chase ();
				animation.Play("walk");

			}
		} 
		else 
		{
			//enemy doesn't see you
		}   
	}
	
	
	
	// Turn to face the player.
	void  lookAt (){
		// Rotate to look at player.
		Quaternion rotation= Quaternion.LookRotation(Target.position - transform.position);
		// Dampening will slow the turn speed of enemy.
		transform.rotation = Quaternion.Slerp(transform.rotation, rotation, Time.deltaTime * Damping);
		//  transform.LookAt(Target);
	}

	
	void  chase (){
		//animation.Play("walk");
		moveDirection = transform.forward;
		
		moveDirection *= moveSpeed;
		
		moveDirection.y -= gravity * Time.deltaTime;
		controller.Move(moveDirection * Time.deltaTime);
	}
	void  attack (){
				//animation.Stop("walk");
				
	}
}

It looks like you don’t have an else if for either of your animation conditions. Therefor one can easily overwrite the other.

I would set up a bool for when the attack should start and also for when the attack should finish.

You just need to ensure that any one animation cannot interfere with another one unless it’s supposed to. For example a death animation would likely overwrite any other logic.

I answered a similar question recently with a fairly detailed example you could start there.