Some, including me and Norwich, laid the blame for the equaliser with BNC (for not covering the 1-2) and Cooper (for losing his man) but having seen the goal feel that Billy contribution was greater than I originally thought.
Let me explain. Billy was brought on to replace Casper (i.e. right central midfield); he had the ball circa 5 yards from the left touch line and 5 yards into our half (i.e. NOT RCM). This should not have been a problem if he had played the simplest (and safest) pass to Longman (who was unmarked to his left) but no, he tried a step drag back, lost possession which, in effect, took both him and Longman out of the game.
Watford swung the ball to the right, BNC picks up the player Billy should be marking that exposed Danny to the 1-2 (that he tried valiantly to defend but failed) and cross that was headed home.