On first blush this decision is a tad confusing.  Legal malpractice plaintiff sues his former defense attorney who defended him in a cross-over head-on car crash.  Plaintiff in legal malpractice case had driven the cross-over car, and had no memory of the accident.  After he loses the car crash case on summary judgment, and then sued the other driver in a second case, he sues the attorneys. The case is Luscher v One Beacon Ins. Group ;2009 NY Slip Op 29076 ;Decided on February 25, 2009 ;Supreme Court, Kings County ;Kramer, J. 
 So far, simple.

Attorneys seek to depose victim of car crash case, in legal malpractice case.  Theory against target attorneys is that they failed adequately to oppose summary judgment with an affidavit of a person with knowledge.  It appears from this decision that only the two drivers have actual knowledge.

Court denies deposition.  One might think this a defeat for attorneys?  We don’t think so. Once it is determined that no one has actual knowledge of how the accident occurred, we think the defense has undermined the plaintiff.  Here is the court:

"Defendants argue that they need to depose Arrua in the instant action because he was never actually deposed with respect to liability in the predicate action and the affidavit he submitted with his summary judgment motion did not provide any information about the details of the collision; the lights on the road, the traffic signs, the speed of the vehicles or whether he uses glasses or contacts and whether he is familiar with the area. Defendants argue that this information cannot be obtained from other sources because their former client, Luscher, did not have any memory of the accident.[FN4] The witness argues that the facts and circumstances of the underlying accident were already decided in the predicate action and consequently the defendants are barred by the doctrine of collateral estoppel from taking his testimony.

In order to defend a legal malpractice action, the defendants must show that they were not negligent or that their negligence was not the but for cause of the plaintiff’s failure to prevail in the underlying action. (Wray v. Mallilo & Grossman, 54 AD3d 328[2d Dept. 2008]). The appropriate analysis in a legal malpractice case does not include or permit a collateral attack upon the underlying judgment. Thus although New York’s liberal discovery rules require "disclosure upon request of any facts bearing on the controversy," Allen v. Crowell-Collier Publishing Co., 21 NY2d 403[1968], the discovery of facts and circumstances whose sole purpose is to launch a collateral attack on the underlying judgment by revealing possible defenses to the predicate action does not fall within this rubric. The information sought to be obtained from this witness with respect to the circumstances attendant at the time of the collision would serve only to undermine the judgment in the predicate action and thus is not relevant [*3]here. "