It would help if you elaborated a bit on what your pictures looked like.
One problem can occur if you use flash while it rains; you can expect to have very bright raindrops close to your camera that will be very much overexposed and very likely out of focus. At slower shutterspeed, the raindrops will look like bright streaks; at faster speeds they will look like blobs. Hope this helps.

Frans Waterlander
frans2001@netzero.net

My pics were very underexposed. The only thing that I did not try was using the flash. I tried changing the speed, using the shutter mode, using the aperture mode, and the p mode with no success. In some of the modes they were extremely dark and others were usable with alot of noise.

Flash is of no help if your subject is farther away than the flash's reach, which is surely the case in outdoors sports and the camera's built-in flash. Good that you didn't use it because it woul only cause the overexposed raindrops that I refered to.

Maybe there just was not enough light to make a decent shot no matter what. You could try aperture mode, open up your lens all the way and play with the ISO value untill you get a decent exposure or use auto-ISO. Noise/grain will increase rapidly as you use a higher ISO value.

Frans Waterlander
frans2001@netzero.net

I cannot speak for the rain issue but I shoot many professional football games per year and this is how I do it. I shot most of my shots with my D70 but the key was buying a good and heavy lens. I have the Nikon 80-200 2.8 and shoot in "Aperature Priority" so the backgrounds look foggy and the subject is the main thing you focus on. I learned my lesson with other lenses the way you did. I tried an 80-400 4-5.6 but as it got darker I was basically out of commission.

Posting a picture would help find the cause of the under exposure. I would, at this point, guess that your metering was at fault. If there were a large expanse of sky, the subject, the football player may be under exposed as the camera would meter and expose for the sky. Perhaps spot metering the player would help.

Still waiting to read what camera and lens you were using. It should have been explained in the initial post where you were asking for help.