I suspect the debate over whether judges are like baseball umpires is as old as baseball itself, but here’s an early example I came across on Westlaw:
A well-known English judge, watching village children drawing up rules for their cricket team for the year, said they were showing him how the common law of England was made. I venture to think that this view is not quite correct. The common law was no set of rules purposely drawn up for the governance of the community but rather a set of customs which evolved into form in the course of years. Now and then, indeed, the sovereign power intervened to modify the old rule or prescribe others; but in most cases where the judge was called on to give a decision he was not like the umpire at cricket or baseball, sent to his body of formal and fixed rules to find out what should govern and to decide according to the rule prescribed; he was rather like the friendly arbitrator deciding according to what he considered the requirements of decent neighborhood, that is “the customs of the country”-Sittlichkeit, if you will. Every time he made a decision, he made the custom more definite. He did not, indeed, affect to lay down any new rule or to govern himself by any but the existing sense of the community-that is, what was just and right in the particular case, bearing in mind the customs which were followed and which fixed rights and duties, more or less indefinitely indeed, but nevertheless fixed them. But every time, he used his own sense of what was just and right in the particular case.
William Renwick Riddell, Common Law and Common Sense, 27 Yale L. J. 993, 995-996 (1918) (emphasis added).