Physics of slapshots in Ice Hockey We have two ice hockey players and a puck. Let's call them $P_1$ and $P_2$.
Worlds fastest recorded slapshot has been around 177 kph, but the puck has been stationary during the shot.
Let's assume that $P_1$ is at the blueline facing towards the goal. $P_1$ makes a fast pass towards the left side faceoff spot where $P_2$ is not stationary and ready for one timer shot. $P_2$ makes a one timer slapshot and shoots the puck to the goal.
Will that kinetic energy of the puck help $P_2$ make a faster slapshot?
Could one make much faster shot (than the world record) with help of a pass from other player?
 A: Yes. this is possible. Here is a highly simplified explanation :
Suppose the 1st player swings his stick towards a stationary puck with speed $u$. In the frame of the player the puck moves towards him with relative speed $u$. Assuming that the stick and player are rigidly connected and very much heavier than the puck, then in the player's frame of reference his rebound speed is very small. Only the puck rebounds with significant speed. If the collision is elastic then the puck rebounds with the same speed $u$ relative to the player as when it approached. In the ground frame of reference the puck moves forward with speed $u+u=2u$.
The puck moves towards the 2nd player with speed $2u$. This player also swings his stick towards the puck with speed $u$. In the reference frame of the 2nd player the puck approaches with relative speed $2u+u=3u$, and in this frame it rebounds elastically with speed $3u$. Relative to the ground the puck leaves the 2nd player with speed $u+3u=4u$. 
The rebound shot from the 2nd player travels at twice the speed which the 1st player was able to give to the puck.
In this example the 2nd player hits the puck straight back to the 1st player. If the 2nd player hits to the side the final speed will be less than $4u$ but still more than $2u$. 
In theory the two players could continue hitting the puck back and forth between them, increasing the speed of the puck indefinitely. In practice energy losses during the collision will increase as the puck and stick become permanently deformed instead of storing all of the kinetic energy of the incoming puck as elastic energy.
The slapshot in ice hockey involves storing energy in the stick before it makes contact with the puck - like flicking a finger at something compared with pushing your finger at it. This increases the speed of the stick $u$ when it collides with the puck.
In tennis, the return can be faster than the serve. However, the record for the fastest serve is higher than for the fastest return because of limitations of controlling the ball at high speed. A shot launched downwards over the net from a racket length above head height has a shorter range than a ball launched from chest height with the same speed. It is much more difficult to keep a fast return within the court. 
A similar question : Can a collision of 2 objects result in one object having a higher velocity than either object had before they collided?
