How to capture value of a field in a node
What u can do is, pass leg_id in the function definition, like:

function get_committees($leg_id = '') {
if(empty($leg_id)) {
$leg_id = 'NCL000208';
}
...


and in the content of block inside block_view, u can call this function, with leg_id, if u are sending leg_id through url, then u can get the leg_id from url using arg() function, and then passing it to function.

But since u want to get Leg_id from node, what u can do is:

if (arg(0) == 'node' &amp;&amp; is_numeric(arg(1))) 
$nodeid = arg(1);
$node = node_load($nodeid);
$field_leg_id = $node-&gt;field_name_field_leg_id['und'][0]['value'];


and sending $field_leg_id to function get_committees($field_leg_id)

// Edited

You can do the same by calling menu_get_object(), it will return you an array, what u can do is:

$menu_obj = menu_get_object();
$leg_id = $menu_obj-&gt;field_name_field_leg_id['und'][0]['value'];