var Ball = Container.expand(function () {
	var self = Container.call(this);
	var ballGraphics = self.createAsset('ball', 'Juggling Ball', .5, .5);
	self.speed = 0;
	self.move = function () {
		self.y += self.speed;
		self.speed += 0.1;
	};
	self.bounce = function () {
		self.speed = -20;
	};
});
var Footballer = Container.expand(function () {
	var self = Container.call(this);
	var footballerGraphics = self.createAsset('footballer', 'Footballer character', .5, 1);
	self.speed = 10;
	self.moveLeft = function () {
		self.x -= self.speed;
	};
	self.moveRight = function () {
		self.x += self.speed;
	};
	self.kick = function (ball) {
		if (ball.y >= self.y - ball.height && ball.x >= self.x - ball.width / 2 && ball.x <= self.x + ball.width / 2) {
			ball.bounce();
		}
	};
});
var Game = Container.expand(function () {
	var self = Container.call(this);
	LK.on('keydown', function (obj) {
		var event = obj.event;
		if (event.key === 'ArrowLeft') {
			footballer.moveLeft();
		} else if (event.key === 'ArrowRight') {
			footballer.moveRight();
		}
	});
	var ball = self.addChild(new Ball());
	ball.x = 2048 / 2;
	ball.y = 2732 - 100;
	var footballer = self.addChild(new Footballer());
	footballer.x = 2048 / 2;
	footballer.y = 2732 - footballer.height / 2;
	var score = 0;
	var scoreTxt = new Text2('0', {
		size: 150,
		fill: "#ffffff"
	});
	scoreTxt.anchor.set(.5, 0);
	LK.gui.topCenter.addChild(scoreTxt);
	var isGameOver = false;
	LK.on('tick', function () {
		footballer.kick(ball);
		if (ball.speed < 0) {
			score++;
			scoreTxt.setText(score);
		}
	});
	LK.on('tick', function () {
		ball.move();
		if (ball.y > 2732) {
			isGameOver = true;
		}
		if (isGameOver) {
			LK.effects.flashScreen(0xff0000, 1000);
			LK.showGameOver();
		}
	});
});

===================================================================
--- original.js
+++ change.js
@@ -27,9 +27,10 @@
 	};
 });
 var Game = Container.expand(function () {
 	var self = Container.call(this);
-	window.addEventListener('keydown', function (event) {
+	LK.on('keydown', function (obj) {
+		var event = obj.event;
 		if (event.key === 'ArrowLeft') {
 			footballer.moveLeft();
 		} else if (event.key === 'ArrowRight') {
 			footballer.moveRight();