If a team receives an overpass it should be a kill 90% of the time.  An overpass is an opportunity to grab momentum as well as score an easy point.  Because the defense does not have an opportunity to set up, and generally there is no block overpasses are an opportunity for a high percentage kill.  The are two basic times when overpasses will occur, directly off serve receive or when the other team is playing defense.  The ideal situation is serve receive, there is nobody at the net, except for the setter and everyone is scurrying around the court to get in position to hit.  In defense the ball may come back over the net before the blocker has time to transition off the net.  They could be able to put up a decent block if they find the ball going over the net quick enough.
   The common errors associated with hitting over passes are: contacting the ball over

the net, touching the net on the follow through and letting the ball penetrate too far before hitting it.  Two out of three of these errors involve some judgment from the official, and anytime judgment is involved the right call is not always going to be made all of the time.  So it is important to attack the ball in such a manner that there is no doubt the contact was clean and also while the ball is in the plane of the net.
   There are two ways to attack an overpass.  Both are shown to the right.  The first is a swing, like attacking with one major difference: no follow through on the arm swing.  On this attack the hitter will swing high and hard snapping the wrist at full extension of the elbow and snapping the wrist.  Upon completion of the swing the arm should still be above the head and the wrist should be snapped fully.  This does a few things, the first is it gives you a good quick attack without an approach.   It puts some pop on the ball without a full arm swing.  This swing allows the hitter to hit the ball down.  It shows the official that there is no way you could have hit the net on the follow through and the ball was contacted it on the hitters side of the net.  The swing is most effective against an over pass in server receive with no blocker in front of you. 
   The second method for attacking an overpass is the power block.  This method is effective because it allows you to control the direction of the attack away from blockers and defenders while still showing the official a legal play.  This attack is done by jumping like you are blocking, surrounding the ball with both of your hands and then just directing the ball to an open area of the court.  There is less timing involved than an arm swing so it is a easier to control the ball.  This method is particularly effective when there is a blocker in front of you because it allows to maintain your strength on the ball even if a blocker should touch it, you just continue the push through the blocker and off their hands.
   Attacking overpasses is a skill like any other.  Mastering the skill takes practice and an understanding of the situation surrounding the attack.  These can be easy kills and momentum grabbers so it is important to take advantage of these opportunities.