Lesson 21 Game not running

Student said his game was working fine and when he added the levelDifficulty function line 316 the game stopped working completely. I had him try taking the code out and it still wouldn’t run. Please help.

The issue that I found is that the student is redefining the background function.
They have

function background() { <--- define a new function with the same name
  background("gray"); <---- here is the background that is part of code.org's sutff.

Change function background() to something else so we don’t have the same name.
The game looks pretty awesome!