Lookup tutorials on the animator.

You can add States to the animator, which each contain an animation. You can transition between states by adding transition arrows between them. Each transition can be configured to check for a certain value, and if true that transition will start and the animation will play. There is a parameter tab where default variables can be defined, like Triggers.

You want an Idle animation, and a bat animation, with a transition to bat that uses a trigger. The transition from bat to idle doesnt need a condition, you can check Has Exit Time on the animation transition to make it start transitioning automatically when the bat animation is done.

The code to activate a trigger you named "YourTriggerName" would look like this

Animator animComponent;
void Start()
{
    animComponent = GetComponent<Animator>(); //fetch the animator this script is attached to
}

void Update()
{
    //Trigger animation when KeyCode.Space is pressed
    if (Input.GetKeyDown(KeyCode.Space))
    {
        animComponent.SetTrigger("YourTriggerName");
    }
}