Array (
    Array[0] (
        "name" => "John",
        "score" => 4
    ),
    Array[1] (
        "name" => "James",
        "score" => 2
    ),
    Array[2] (
        "name" => "Mary",
        "score" => 3
    )
    etc
)

<?php

function usort_callback($a, $b)
{
  if ( $a['score'] == $b['score'] )
    return 0;

  return ( $a['score'] < $b['score'] ) ? -1 : 1;
}

usort($array, 'usort_callback');

function cmp($a, $b)
{
   if ($a["score"] == $b["score"]) {
       return 0;
   }
   return ($a["score"] < $b["score"]) ? -1 : 1;
}
usort($a, "cmp");