How to Cure Side Stitches When Running:
From E-How.com http://www.ehow.com/how_4489555_cure-side-stitches-running.html

Many runners at times experience a very painful cramp underneath their rib cage while exercising. This pain makes breathing difficult and moving fast almost impossible.

Instructions:

Step 1
Eat at least two hours before doing any serious exercise. When you eat shortly before exercising, make sure that you do not stuff yourself full of junk food with lots of empty calories. Eat something small with good carbohydrates and some protein. Having some fruit is a good idea, too.

Step 2
Drink lots of water. Water is one of the key things that your body needs to have when exercising, especially if you will be in the heat. Without sufficient water and minerals in your body, you will not perform as well. However, do not chug water right before you exercise because this will give you cramps.

Step 3
Stretch your muscles before you do any physical activity. Sometimes having tight muscles can cause side stitches and other types of pain to occur more easily. Stretch your calves, your thighs, arms and other parts of your leg. Try to hold each stretch for a minimum of 10 seconds.

Step 4
Steady your stride and try to find your breathing pattern when running. Instead of going fast then slow or having short quick strides, try to even out the strides and maintain one steady pace. Don’t sprint during a long run; instead, try to go at a fast jog.

Step 5
Exhale when you land on your left foot. Many runners breathe about every fourth stride. A good breathing pattern is to take a very deep breath then run four strides. As your left foot lands, breathe out, then repeat the pattern.