What would be the thing to do if a child has sudden cardiac arrest while playing a sport on the field?

Swift action: Put in play your abc's (airway, breathing and circulation) as fast as possible. If you determine that the child has a clear airway, is not breathing and has no pulse initiate CPR right away and instruct one specific individual to call 911 (don't just say, "someone call"). Should there be a defibrillator available delegate the use of the device to someone who knows how to use it at once.

Call 911: Start CPR immediately after calling 911. If a AED is available hook it up and follow the directions. Learn CPR and take refresher courses to keep up to date.

CPR...: If anyone, including a child, has a sudden cardiac arrest, 911 should be immediately called and CPR initiated. The 911 operators can talk you through it if you are untrained. An automatic external defibrillator, or aed, should be applied according to the directions if one is available. This device will deliver a "shock" to the heart, if warranted. This can all be life-saving.