A side stitch (where you feel a sharp stabbing pain under the lower edge of the ribcage) is a common ailment while running. Yight be able to avoid that simply by changing your running gait to always breathe in and out on your left foot.
Photo by Mike Baird
That's the suggestion of Dr Tim Noakes in his book The Lore Of Running. Drawing on Dr. Noakes' advice, the authors of 100 Questions and Answers about your Sports Injury further explain what you need to do and why:
Change your gait such that you are beginning inhalation and exhalation as your left foot strikes the ground. Many runners begin and end their breathing cycle on the same foot, such that runners may be described as right-footed or left-footed with regards to breathing. Practising this altered gait may decrease the frequency that the liver, the heaviest abdominal organ, is displaced downwards while the diaphragm is in its highest position.
This advice goes against the 3:2 inhale-exhale ratio for improved runs, but preventing a side stitch might be worth it. If you still do suffer from that pain, there's a three-minute fix to get rid of it.
100 Questions & Answers About Your Sports Injury [Google Books]