Edit in JSFiddle

$(document).ready(function () {
                $("#main li").hover(function () {
                    $(this).find("ul").slideDown("slow");
                }, function () {
                    $(this).find("ul").slideUp("slow");
                });
            });
<html>
        <head>
        <title>Slide Effect</title>
        </head>
        <body>
        <ul id="main">
        <li>Football
        <ul class="innerList">
        <li>Fabregas</li>
        <li>Henry</li>
        <li>Messi</li>
        </ul>
        </li>
        <li>Cricket
        <ul class="innerList">
        <li>Sachin</li>
        <li>Ponting</li>
        <li>Sehwag</li>
        </ul>
        </li>
        <li>Tennis
        <ul class="innerList">
        <li>Federer</li>
        <li>Djokovic</li>
        <li>Nadal</li>
        </ul>
        </li>
        </ul>
        </body>
        </html>
#main li
        {
        float: left;
        padding-left: 20px;
        list-style: none;
        }
        .innerList
        {
        display:none;
        }
        .innerList li
        {
        float:none!important;
        margin-left:-20px!important;
        }