Running

http://www.makeithappen.com/wis/readings/sidest.html

this is what I've always believed was the cause of most stitches. If I feel a stitch coming I tend to slow my breathing by holding in the breath then blowing it out through pursed lips to slow the exhalation and lengthen the in/out cycle and I also to try and alternate the foot i strike with when exhaling and hope it goes away after a few minutes.

Taken this from Wiki and can confirm adjusting your breathing pattern to left foot strikes works for me.
The idea being you are creating space and reducing pressure on your liver.[quote]Most of the time, side stitches occur on the right side of the body[citation needed]. This may be because the largest organ in the abdominal cavity, the liver, is on that side. Certain athletes also report a pain in the tip of their shoulder blade. This is believed to be because this is a referred site of pain for the diaphragm via the phrenic nerve[1][better source needed]. When the side stitch is on the right side, published advice is to try to exhale when your left foot lands.
[/QUOTE]
Switching the foot I exhale on to stop stitches? Sounds like rubbish, but I'll give it a go!