Walking and attack animation of character appearing broken

I am trying to make a small game where a zombie follows the player and attacks on getting near. But it is appearing broken. Here is the video:

Here is my code controlling the Zombie:
void Update()
{
agent.SetDestination(player.position);
if (agent.pathPending)
return;
float speed = 0.0f;
if (agent.remainingDistance <= agent.stoppingDistance*stopDistanceProportion )
{
agent.isStopped = true;
animator.SetBool("PlayerClose", true);

transform.LookAt(player);
}
else if(agent.remainingDistance < 50.0f)
{
float proportionalDistance = 1f - agent.remainingDistance / agent.stoppingDistance;
transform.LookAt(player);

speed = Mathf.Lerp(0.5f, 1f, proportionalDistance);
agent.isStopped = false;
animator.SetBool("PlayerClose", false);
}
else if (agent.remainingDistance < 150.0f)
{
Quaternion targetRotation = Quaternion.LookRotation(agent.desiredVelocity);
float proportionalDistance = 1f - agent.remainingDistance / agent.stoppingDistance;
transform.LookAt(player);
speed = Mathf.Lerp(0f, 0.5f, proportionalDistance);
agent.isStopped = false;
animator.SetBool("PlayerClose", false);
}
else
{
agent.isStopped = true;
animator.SetBool("PlayerClose", false);
speed = 0f;
}
animator.SetFloat("Speed", speed);

}
The zombie starts attacking animation when "PlayerClose" is set true and the Speed is used to control walking, running and Idle. Idle on 0, walk on 0-0.5 and run on 0.5 to 1. So why is this happening? I am new to Unity animations, so please guide me.

 

Hey look into your animator controller. Open it up and look at the transitions you can change the amount of time it takes to blend between two animations, and you can also adjust the exit time. It may just be the animation is exiting early or the transitions is too long between animations. This can be changed by clicking on the transition lines in the animator window.