As NHL defensemen become more mobile and offense-minded, teams are giving them permission to join the rush and turn a typical 3v3 line rush into a 4v3. D1’s presence in the middle allows F1 and F2 to overwhelm the strong-side defenseman and create a mismatch on entry. Note that D2, the last man back, may have to defend a 2v1 against if the attacking team turns the puck over at the blue line.