I had just moved to a new house, just up the street from my high school. Our high school has a huge field in the back, for football, soccer, baseball, etc. I had two friends over, who I will refer to by their first initials, A and J.
So, it's around 10:30, and we're all sitting around my house, when we decide to walk over and explore the field at night. No flashlights except for the single LED flash on my phone. We set off into the field.
We're walking across the field, getting closer to the tennis courts, beyond which is the track. Between the tennis courts and the track are a row of trees or really tall bushes, planted fairly close. We know a bunch of tennis balls usually get lost in this area, so we start looking for tennis balls to keep or toss around. While looking around on the ground, we could swear that we heard some light footsteps behind us. I was the farthest back in the group, A and J were farther ahead. I turned around, and immediately the noise stops. I look around some, and don't see anything. By this point, I've backed up to where A and J are standing. They had heard the noise too, and we decided that it wouldn't be that great of an idea to hang around the area. We walk along between the line of trees and the fence of the tennis courts, eventually coming to the gate leading to the track.
The gate is locked, so we decide to not try to get inside. However, just to the right of the gate, there's a small building. It's about 8 feet per side, peaked roof, not connected to anything as far as we bothered to find out. On the side of the building we were facing, there was a door. A heavy-duty, metal door with no handle or other visible means of opening it. Right above the door there was a yellow light shining down, and in the light, we could see a splash of some liquid on it, running down. The liquid was slightly darker than the light brown of the door, and no longer wet. It had dried on the door. There were strange, tiny chunks of something in the liquid as well. Because of the light, there were a lot of moths around, and they seemed to be almost eating the liquid. Aside from the splash, the door was covered with dents, seemingly clustered around three feet up from the ground. Listening inside, we could hear a sort of clanking sound, like chains or old machinery.
Justifiably freaked out, we left there, sprinting away across the field. By this point, we had drawn nearer to the school, and we wanted to avoid any potential people inside from seeing us. When we had gotten about a third of the way across the field between the building and the other side where my house is, we stopped sprinting and got down low in the grass. A mentioned it first, a feeling of being followed, of someone walking along behind us, slowly. A few minutes later, I felt it too, then J as well. We couldn't hear anything, and we were all breathing slightly heavier, from the combination of the sprinting and adrenaline. We didn't see anyone or hear anything, but we could all feel someone or something there, moving slowly, methodically, after us. We got up, staying crouched, and moved across the field.
We made it back to my house around 11:30, and A went home around 11:45. We still have no idea what happened that night, and we're planning on going back there, possibly with cameras, to record the building.