A javelin is an ancient weapon meant to be thrown into heavy soldiers, meant to break their formation to weaken them. For this event, you will throw one such weapon as far as possible.
Continuously tap the fire button to build up speed. As you approach the throw line (specifically at the second meter marker before of the line), press left to start your aim.
The best aim should have the javelin either aligned with the stadium, or just below the top of the screen. If it is too high, it won't have enough horizontal velocity. If it is too low, it won't stay in the air long enough.
The world record is 91.06. To claim the new record for your disks, you need to be running at full speed when making the throw, and find the optimum angle for the javelin.