How do I update a field with result of a Select Count Query?

 
The query is named CountnumIn(@EventID) in the table adapter.  It is called after a player is added to or deleted from an event in the t_Committed table.  The adding and deleting is handled by a ListView2 control.  The field to be updated is numIn in table t_Event
SELECT     COUNT(*) AS numInCount
FROM         t_Committed
WHERE     (EventID = @EventID)
 
...