There are three open field battles on Friday. They are officially scheduled to last half an hour each, but of course the actual time will depend on how the fighting goes. The battles must have a clear-cut winner, so they go on until one side or the other is unmistakably eliminated. Like most SCA battles where even the casualties can walk away, it's common for them to go to literally the last man.
      There are supposed to be 3 battles this year. The first will include combat archery, and the second will not. The third battle will be fought only if there is a tie after the first two, and if it does go on it will also include combat archery. There are no siege weapons allowed in any field battles.
      The field slopes so the eastern end is about 20 feet higher than the end closest the fort.  This does make a little difference when you're charging in armor.

      As far as its effect on the course of the fighting, combat archery in the field battles has so far been more annoying than important. The numbers of archers have so far been too low for mass firings. Also, the action between the armies flows at such a rate that archers usually spend more time moving than sighting on targets.
      For finding targets to engage, the archers' best bet is to stand wide of the formations, to get angles on opposing unit flanks where shields and friendly troops don't intervene. Of course, this generally exposes the archers, leaving them liable to be charged by opposing flankers. For full effectiveness, archers need to organize in sizable bodies, and coordinate with friendly fighters to provide front cover. Whenever possible, they should maneuver to take opposing units in defilade, so they can fire down the length of the formations for maximum hit probability.
      Shooting toward the road on the northern side of the battlefield is tricky. Spectators come right up the the edge of the road, and long shots could easily fly into the crowd. Archers who facing the northern side of the field must be very careful about their angle of fire and their elevation.

For more information about combat archery, follow this link.