The Lee Williams try should never have happened, it resulted from a Welsh scrum that should in fact have been a Scottish scrum. Visser caught the high ball and was then held up in the tackle but when it's from a kick the referee should award the scrum to the catcher's team. Big mistake by the referee but fortunately it didn't cost Scotland the match. Bad enough that players (English ) don't know the laws of the game but referees should.