When will a judge order a competency hearing against a defendant?

When the trial court is presented with substantial evidence of incompetence, it has no discretion to exercise, and it must, as a matter of law, initiate proceedings to determine whether the defendant is currently competent to stand trial. (Mai, supra, 57 Cal.4th at p. 1033 [trial court has discretion to decide against a competency hearing only "absent a showing of 'incompetence' that is 'substantial' as a matter of law"]; People v. Welch (1999) 20 Cal.4th 701, 738 ["once the accused has come forward with substantial evidence of incompetence to stand trial" the trial judge "has no discretion to exercise"].)