var theAnimation : AnimationClip;

function OnTriggerStay () {
    if (Input.GetKeyDown("e")) {
        animation.Play();
        //Other actions here
        if (audio) {
        audio.Play();
        audio.loop = false;
       }
        }
    }

or try downloading Dastardly banana's weapons package and use their weapons system because they have a melee weapon so u can set it to play ur punch animation