Kinect Sports

Tried the solutions here and may have found an easy way. Similar to one other here;

1) simply outstretch your arm and keep it in this position.
2) Now simply turn on the spot (pivot on one foot) slowly and keep your arm facing outwards. Essentially you are just turning your body to the left or right depending on your preferred hand.

Just about every throw will be around the 4 meter mark. Pivot as slow as you can to reduce throwing distance. It might even work better if you drop your arm while pivoting too but I did not test this at the time.

[16 Dec 2010] TIP COURTESY OF CrazyC0330:
IF YOU WANT TO FOCUS ON THIS ACHIEVEMENT AND NOT OTHER TRACK & FIELD CHEEVES, LOAD UP THE DISCUS MINI-GAME AS A QUICK ALTERNATIVE TO PLAYING THROUGH THE REGULAR GAME!
[Thanks, CrazyC0330]

In order to get less than 4 meters, the discus has to hit inside of the dirt (brownish red area) immediately in front of you. It has to hit a little less than halfway between where your avatar stands and the start of the green grass area. Since the Kinect sensor picks up any forward movement and counts that as a throw (my first attempt at a bad throw still went 10 meters), you must "throw" your discus and move your arm directly at the ground while going forward.

Best chance to do this is to drop your arm almost straight down from an outstretched position. Key is that you have to act like you are throwing it directly at the floor in front of you (for real!). It took a few attempts for me and I hit right at 4.00 meters, but the achievement will not unlock there. Must be LESS than 4 meters. Keep "throwing" at the floor and it should unlock after a few attempts.

What I did to get this one was crouch and move my arm just hard enough so kinect would register my movement as a throw, got it on the first try

To achieve a throw of less than 4 meters for the achievement to pop even tossing a weak throw at the ground directly in front of you can prove a bit challenging.

I was able to knock this off by throwing the discus into the cage immeadiatley around you. The throw counts as a foul but the achievement still pops and let's be honest if you were trying to throw less than 4 meters you shouldn't really be worried about incurring a foul ;)

For this, be sure that you step back as far as you can but staying inside the throwing area. This can help if you keep getting a bit over 4 meters and haven't done so already.

As said previously use the discus mini game. Then hold your arm high in the air, swing it downwards accross the front of yourself towards the floor. Dont swing your arm forward.