Triathlons
Running is the last leg of any common triathlon. Triathlons usually consist of three events in this order: swim, bike, run. Distances are event specific.
For an Ironman triathlon, the running portion is a full marathon (26.2 miles). For other triathlons, the running portion can vary from less than 2 miles, to 13.1 miles.
Triathlete is a great place to investigate competing in a triathlon.