Going up to support somebody in the marathon and looking for something to do? Not running the marathon but still want to be part of the weekend action? Try the BAA 5K on Marathon Sunday. Replacing the Boston Freedom Run, the 5K is a competitive race that starts at Copley Square, loops up and around Boston Common and then returns to finish at the Marathon finish line. Registration will take place entirely on-line beginning at 9:00AM on the 3rd of March and the race is expected to reach its 5000 person cap quickly.