"By rule"? I don't know that one - I'm not trying to be clever, but I don't. What's the penalty for violating it?
I may be a bit naive with this topic but it seems to me the intent should not be that you may or may not be showing up another ump or not, or undermine his standing. To me it would seem more important that the correct call is made regardless of responsibility. If you have a better view of a play why does it matter who makes that call. You see it all the time in other sports (and when I reffed football it was fairly common) for one official to either over rule or talk it over if they have the better view. I don't know seems a vestige of some bygone error. Just my humble opinion.
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