Two things makes this non working.
First: You need to randomly pick something from the array. I added this line to do that
Code:
var random = arySports[Math.floor(Math.random()*arySports.length)];
Second: Your words start with a capital. If the players does not capitalize there will be no match so I made everything lower case.
The code:
Code:
<script type="text/javascript">
var Guess;
var arySports = new Array("Football","Basketball","Rollerblading","Hiking","Biking","Swimming");
var random = arySports[Math.floor(Math.random()*arySports.length)];
Guess = prompt("Guess a mystery sport", "")
if (Guess.toLowerCase() == random.toLowerCase()){
alert("Congrats");
}
else {
alert("Please pick again")
}
</script>