In what circumstances will a court overturn a jury's finding that negligence was not a substantial factor in causing injury?

Similarly, in Zecher v. Backus (2001) 730 N.Y.S.2d 898 [286 A.D.2d 884] (Zecher), the jury found both negligence and injury, but determined that the defendant's negligence was not "'a substantial factor in causing the plaintiff's injury.'" (Id. at p. 899.) The trial court concluded this finding was against the weight of the evidence because "[t]he testimony of [the] plaintiff's treating physicians established that the accident was at least a substantial factor in causing [the] plaintiff's injury." (Ibid.) The court properly set aside the verdict but erred in ordering a new trial with respect to damages only. (Ibid.) Citing the rule in Browne, the appellate court modified the order to grant a new trial on both proximate cause and damages. (Ibid.)