Appeal by defendant from a judgment of the Supreme Court, Queens County, rendered December 15,1978, convicting him of manslaughter in the second degree and criminal possession of a weapon in the fourth degree, upon a jury verdict, and imposing sentence. Judgment reversed, as a matter of discretion in the interest of justice, and new trial ordered. The conduct of the prosecutrix in forcing the defendant to characterize the testimony of prosecution witnesses, including a policeman and an assistant principal, as either lies or, at least, mistakes, was improper. This court has repeatedly advised prosecutors that this is a practice which will not be tolerated (see, e.g., People v Perez, 69 AD2d 891; People v Webb, 68 AD2d 331). It was particularly egregious in the instant case where defendant was the sole defense witness and presented a justification defense. All other eyewitnesses, save one, were friends of the decedent. The only witness who testified that defendant made the fatal knife thrust was a friend of decedent’s girlfriend. Thus, the issue of credibility was crucial. The prosecutrix attacked the defendants credibility unfairly by the series of questions indicated. In addition, she asked defendant about a prior incident with a knife without making any showing of a good faith basis. Indeed, questioning about a knife possession charge arising out of that same prior incident had been excluded at the Sandoval hearing. This behavior was so damaging to the defendant that a new trial is required notwithstanding counsels failure to object. Hopkins, J. P., Gulotta, Margett and O’Connor, JJ., concur.