That's part of the task:

Your task is to find out what this is and write a function that will add atwo strings together, there must be a space between the two strings.

It's not directly related to how + or concat work. Also, you can't use them here.

And where does it say it adds a space?

You've destroyed games with splice how is that not mutating the input?

Write console.log(games); as the first line of your code and before your function's return line too, see if they're different, if so, you've mutated the input.

Could you just post your code in a comment with a spoiler tag?

But have you tried not mutating the input?

You're probably mutating the input.

There are 10 matches in the array you need to process.
x and y will not be smaller than 0 or bigger than 4.