Depends on your magnification and how fast people are moving. '500 is a safe bet for a normal lens, but if there is enough light, I try to use '1000 or '2000 if I want totally frozen sharp pix. Also, '500 is *not* a safe bet for a long lens. Soccer is frustrating because the shots could happen anywhere on the field, so a lot of it is luck and lens choice. There will be times in the match where you need a 600mm lens, and times where you will need a 50mm lens. Shooting kids is even harder because you need more magnification to fill the frame with people, and the action is less smooth and predictable.
With your 85, Tri-X, and late afternoon Florida sun, I would assume approx. F/8 to f/11 at '250 to be a decent exposure to start, assuming EI 250. So I might shoot at f/2 or f/2.8 at '4000. As the day goes on, you can lower your shutter speed to add light. I would not bother shooting unless the action is near enough. You won't be able to see anything anyhow if you shoot really loose and then crop. Depending on many things, the action could be within range of your lens for reasonable lengths of time, or it could not be. Good luck on that part of it!