As the centre of mass of javelin follows parabolic path, the javelin also rotates about it’s centre of mass while in air. As a result, it hits the ground with it’s nose. Where is this angular momentum coming from? Is there some torque acting on the javelin? Or, Is the angular momentum simply imparted by the athlete when he throws the javelin?
Please see the related post here. The answer lies in the the wikipedia section on the modern redesigns for javelin throw competitions. It states that
In 1986 the technical committee of the International Association of Athletics Federations introduced new specification for the standard competition javelin. Among other things it was specified that the center of mass should lie forward of the center of air resistance. This new specification gives a nose heavy javelin. The previous standard competition javelin was designed to be balanced. When thrown with perfect balance the javelin would keep climbing for a long time. More and more often the javelin would hit the ground while parallel to the ground, and would continue to slide for a distance. The javelin throw event became rather dangerous; sometimes the sliding javelin would slide all the way onto the running track.
Overall, as the spear moves through the air, aerodynamic friction on the spear affects it's path. Since a completely symmetric spear is unlikely and difficult to realize, besides being unnecessary for the function of a spear, the aerodynamic friction applies a torque on the spear, thus causing it to rotate.
With regards to the new redesign, a balanced javelin is more unforgiving since one has to throw it just right, else the throw would not be curved as desired. On the other hand, the new javelin tends to self-straighten in flight, so the throw no longer needs to be perfect. This redesign therefore shifts the focus from throwing skill to throwing power.