Bk9iq - damage dealing

/*PlayerScript.js*/

var enemiesInRange:Array = new Array();

function OnTriggerEnter(other:Collider){ //Detect any object with a trigger Collider entering the trigger's radius
    if(other.tag == "Player"){ //Check the tag set in Unity's inspector. If it's another player:
         enemiesInRange.Add(other); //Add it to the list of enemies in range.
    }
}

//Now let's also make sure to clean up after they're out of range!
function OnTriggerExit(other:Collider){ //Detect any object with a trigger Collider entering the trigger's radius
    if(other.tag == "Player"){ //Or check if it's currently in the array.
         enemiesInRange.Remove(other); //Remove it to the list of enemies in range.
    }
}

function Update(){
    if(Input.GetButtonDown("YourAttackButton")){ //Attaaaaaaack!!
        for(var enemy:Collider in enemiesInRange){ //Remember, we stored the other players' Colliders' only
            var enemyScript:PlayerScript = col.GetComponent(PlayerScript); //Get the other player's PlayerScript (if that's what you called it).
            enemyScript.hp -= 25; //deal 25 hp of damage. Alternatively I'd recommend using: enemyScript.loseHP(25);
        }
    }
}