$array_one = ["Vikings","Eagles","Jaguars","Patriots"];
$array_two = [
    "Vikings"=>1,
    "Eagles"=>1,
    "Jaguars"=>1,
    "Patriots"=>1
]

//Validate using array 1
if(in_array($user_input,$array_one)) {
   echo "Valid Input";
}

//Validate using array2
if(array_key_exists($user_input,$array_two)) {
   echo "Valid Input";
}