Explanatory models of practical reasoning are only as useful as how well they illuminate--provide instructions for--engaging in some practice. In baseball, umpires represent the game's authority--the Major League Rule Book containing its canonical rules, and instructions. Umpires, however, have none of the players' interests. In their official capacity, umpires don't care if a pitch is a ball or strike just as long as they call it correctly. Like umpires in baseball, judges in constitutional adjudication represent the Constitution's authority--the Constitution itself, its canonical rules and instructions. For judges, like umpires, the rules they must enforce are created by the Constitution, legislators, and executives.
The Chief Justice, no doubt, intends this model of judging to depict judges as something more than automatons deciding cases mechanically. But he also intends the model of judging to be conspicuously different from lawmaking. Instead, judges apply laws only after interpreting the relevant constitutional provision. The idea of a judge as an umpire is intended to place significant constraints on judicial interpretations. Umpires must attend to the rules of the game as set down in the Major League Rule Book. Similarly, the judge as umpire requires judges to attend to the constitutional rule book. However, just what counts as the constitutional rule book governing constitutional adjudication is itself highly contested. Everyone agrees the constitutional rule book includes the Constitution, judicial precedent, deeply ingrained traditions, and where possible achieving justice. But even these categories, though agreed upon, defy consensus regarding their content and what implications this content have for controversial circumstances.
Presumably, the Chief Justice requires judges to interpret the Constitution by focusing on prior law, namely, the constitutional text, including the text's original meaning, and the constitutional and governmental structures the text implies. According to the umpire model, the overarching plan of judging is for judges to conceal their own constitutional and policy identities when adjudicating constitutional conflicts. Judges should have no stake in which constitutional interpretation prevails just so long as it's the right one. Once the judge determines the right interpretation, the only remaining task is to decide the case impartially and neutrally according to that interpretation.
Is this model workable? Not likely! Why? Because not even umpires can follow rules neutrally and impartially in any real sense. Any baseball fan, for instance, knows that some umpires have stricter strike zones than others; some have more pitcher-friendly strike zones. Why can't all umpires use the same strike zone when the strike zone is clearly defined as the area mid-level between the top of the batter's shoulders and his belt, and the bottom is at the level just beneath the knee cap"? The answer is simple. The Chief Justice's model conjures up an ideal batter and ideal umpire without accounting for significant differences in both types in non-ideal circumstances, which are the circumstances we're always in. Accordingly, no rule can be applied in the manner Chief Justice Roberts' model demands. Applying rules depends on how the applier understands the rule. Unfortunately for the model of a judge as an umpire, this brings in the particularity of the batter, umpire, and context of the game, that is to say, all the subjectivity that the model is designed to preclude in the first place. Understanding requires education, experience, and judgment. Applying rules, just as following rules, is a human endeavor. The human art of judging requires judges to interpret rules as best they can given their particularized understanding of the rule, its abstract and concrete purpose(s), and the context and goals of creating the rule in the first place. This means the interpreter is much more than a rule-follower. So it is with umpires. Recall Bill Klem, the umpire most like a legal realist judge, who stated categorically that a pitch is "nothin"--neither a ball nor a strike--"'til I call it" a ball or strike.
In constitutional adjudication where the controversies are so much more complex, the question of where the constitutional strike zone is located simply defies anything more than a rather thin conception of neutrality, if even that. The central question is neutrality with regard to what? The correct method of interpretation? The values that underlie the Constitution? The ranking of competing values? The significance of the Founding? Popular opinion? An existing consensus of the elected branches? Any interesting answer to these questions will depend on contested values, values that are not irrational to reject. And these contested values will permit consensus only at a rather high level of generality. Consensus might not be a virtue in poetry or modern art, but it certainly is required if law is to function in the spirit of Chief Justice Roberts' model. Without consensus, at least with respect to constitutional controversies, the constitutional strike zone will remain a figment in the mind of a Robertsian judge-umpire. The judge will rely, by necessity, on his or her understanding of constitutional authorities, methodologies, and contexts of adjudication. Sure, no judge should answer a constitutional question by thinking, "What do I think a good policy would be in this case?" Instead, the judge must pose the question as "What does the Constitution conclude is a permissible policy?" But in asking that question, the judge does not avoid appealing to his or her own particular conception of constitutionalism. Rather than avoid it, no judge can judge without relying on this conception. One needn't be a nihilist or a post-modernist to appreciate this point. All one needs is some sensible understanding of how the language of judgment and practical reasoning function in context.