How can a player exert maximal force on a ball as to increase is velocity.

Since the objective of handball is to score points by throwing the ball in the goals from at least 6 meters out, the players require efficient throw-like kinetic chains. The throw kinetic chain is characterised by the joints in the kinetic chain, which extend sequentially (Blazevich, 2012.) However, that is not to say that there is no overlap in the sequence. For example, while the wrist and knuckle are the final accelerants prior to release of the ball, the shoulder is still accelerating during release (Hirashima, Yamane, Nakamura & Ohtsuki, 2008.) The order of major acceleration in the handball throw kinetic chain is as follows:

Shoulder > Elbow > Wrist > Knuckles > Ball (open end)

For a handball throw, the kinetic chain is open-ended, meaning one end of the kinetic chain is free to move (the ball).  By accelerating each of the segments of the kinetic chain, the momentum is transferred along the arm to the end point (Blazevich, 2012.) and since we have an open-ended chain, as described above, all the acceleration is transferred into the ball, causing a high force to be applied on the ball throughout and at the end of the kinetic chain. This can be described using Isaac Newton's second law in mathematical terms:

 Force= Mass (Ball) X Acceleration (achieved through various stages of the throw like kinetic chain)
 

Although not mentioned in the kinetic chain above, hip rotation plays an important part in creating additional force in the kinetic chain and does so in a couple of ways. Firstly, it makes the arm a longer leaver, thus allowing more distance for the kinetic chain described to accelerate and apply more force to the mass (ball).

This is demonstrated below using two figures. The first shows how far back the ball is with no hip flexion and the second demonstrates how far back the shoulder can move with significant hip flexion.

The second way the hip can create additional acceleration is by simply twisting back in place. This actually applies to all of the tendons attached to the joints described above, at the end of the first paragraph.  When tendons are stretched, they build up potential elastic energy which then recoils at high speed (Blazevich, 2012), thus producing additional acceleration during the chain.