A trapping zone defense that positions one player at the top of the key, three players lined up across the foul line extended, and one player running the baseline. This defensive formation is typically employed to aggravate the offensive perimeter players, forcing them to make bad passes and ill-advised shots.
The most notable proponent of the 1-3-1 zone defense is Michigan coach John Beilein. Despite not having the top recruiting class, he has won everywhere he has coached using the 1-3-1 zone, putting up a 171-127 record as the coach of West Virginia for five years and then Michigan for four.
The 1-3-1 zone defense is most vulnerable at the baseline if the offensive team can swing the ball effectively with crisp passes. The defense can minimize that weakness though by putting an athletic player with incredible motor on the baseline. In the last couple of years, West Virginia-which still uses the 1-3-1 zone even after Beilein's departure-usually occupied that baseline spot with starting point guard Joe Mazzulla.