Question: I was recently party to a preliminary hearing in a criminal case in which a 911 call was played. The content of the 911 call was very beneficial to the defendant. During the hearing, the judge said something to the effect of, "It would be a question for the jury whether the caller was 'being honest.'"

In other words, the judge was suggesting that the caller to the 911 was being disengenuous and deliberately conveying a false impression -- something that I think would never occur to most people because the call seemed completely genuine. Also, the caller would have had no motive to faking their mental state. I got the idea that the judge was looking for some angle to discredit the 911 call out of interest to see the defendant convicted.

In any case, from the judge's remark I got the idea that he might say something like that during the trial, or give the jury an instruction designed to make them think the 911 caller was putting on an elaborate act.

Is a judge allowed to do this?

Answer: 
It is the judge's obligation to instruct the jury w.r.t. believing witnesses. [This](https://govt.westlaw.com/wcrji/Document/Ief97fa32e10d11daade1ae871d9b2cbe?viewType=FullText&originationContext=documenttoc&transitionType=DocumentItem&contextData=(sc.Default)&bhcp=1) is the introductory instruction for criminal trials in Washington, which on that topic says

> 
> You are the sole judges of the credibility of each witness. You are
> also the sole judges of the value or weight to be given to the
> testimony of each witness. In assessing credibility, you must avoid
> bias, conscious or unconscious, including bias based on religion,
> ethnicity, race, sexual orientation, gender or disability. In
> considering a witness's testimony, you may consider these things: the
> opportunity of the witness to observe or know the things he or she
> testifies about; the ability of the witness to observe accurately; the
> quality of a witness's memory while testifying; the manner of the
> witness while testifying; any personal interest that the witness might
> have in the outcome or the issues; any bias or prejudice that the
> witness may have shown; the reasonableness of the witness's statements
> in the context of all of the other evidence; and any other factors
> that affect your evaluation or belief of a witness or your evaluation
> of his or her testimony.
> 
> 
> 

Some such statement will be made in any trial. There used to be a more specific instruction in witness credibility, but it was withdrawn. The general instruction also says

> 
> Our state constitution prohibits a trial judge from making a comment
> on the evidence. It would be improper for me to express, by words or
> conduct, my personal opinion about the value of testimony or other
> evidence. I have not intentionally done this. If it appeared to you
> that I have indicated my personal opinion in any way, either during
> trial or in giving these instructions, you must disregard this
> entirely.
> 
> 
> 

Except for Texas and West Virgina, all states have such instructions. If a judge went off the rails and said "You are going to have to decide if you believe all that stuff that Smith said", that would be reversible error. The judge may not imply belief or disbelief, and may not make comments that tend to favor the defense vs. the prosecution.
In the US, in most if not all states, the Judge at a jury trial may not comment in such a way as to indicate a belief in the truth or falsity of testimony or the guilt or innocence of the accused.

I believe the rule is different in the UK and perhaps elsewhere.

However this was not in the presence of a jury.

**Addition**:
This is because in a jury trial, the jury, not the Judge, is supposed to determine the facts. The drafters of US Procedure apparently thought that any comment by the judge would be highly influential with the jury. I think that this was a reaction against 17th C and 18th C British practice.

In England and Wales at least it used to be the case that the Judge would routinely comment on the evidence, both during the course of the trial, and during the "Summing uP" which followed the evidence but I think came before the arguments of the lawyers. I am not sure if theis is still the procedure.