Don’t allow JavaScript in the content area

You could use the_content filter:

add_filter( 'the_content', 'remove_script_tag' );

function remove_script_tag( $content )
{
    return strip_tags( $content, '<script>' );
}

When you also want the content of the tag to be removed you could use this one:

add_filter( 'the_content', 'remove_script_tag_and_content' );

function remove_script_tag_and_content( $content )
{
    $striped_text =  preg_replace('@<script>.*?<\/script>@si', '', $content);
    return $striped_text;
}