Both of the deviants before me gave really excellent responses so there's not much more to add. But I will say this...I shoot sports exclusively and I've managed to do so on the professional level with a five hundred dollar camera body. Right now you can get an introductory level Canon DSLR/Nikon camera with great starter lenses for around five hundred US dollars, which could easily handle the infrequent football game that doesn't need to be a masterpiece.
Since you're already considering an upgrade, do that. There is an enormous leap in quality between a coolpix and a real DSLR. If this is a hobby and will remain a hobby, there's absolutely no need to fork over wads of cash for a pro grade body or super fast glass. The job you're talking about can be done with an entry-level consumer camera body, and I'm proof of that. Fast helps ( 8+ fps), but it's mostly unnecessary for slower sports or those who can anticipate the shot. Which, in my opinion, is everything. I consistently nail the shot just as often as the guys with the enormous expensive cameras do because I know the team and I know the sport and I know that arena backwards and forwards. I highly recommend going to team practices, getting to know the players, checking out the pitch, figuring out where the sun will be, where the lighting will be, beforehand.
If however...as a result of this experience...you get the sports-bug like I did, you may want to spend a couple thousand more and get a great mid range camera like a Canon 7D or Nikon D7000 both of which handle sports very well, but won't have you investing your life savings into them until you're ready to. Sports photography is widely considered most expensive field in photography there is and, ironically, sports teams are notorious for trying to get away with not paying for photographs worth hundreds or even thousands of dollars. So, my main advice for you is: don't jump into the deep end of the water and buy expensive equipment unless you're prepared to swim like crazy for it.
Well, I shoot sports for a newspaper and cover a lot of sports - Football/soccer is one of the sports I cover regularly.
I've not used the P90, but there are a couple of issues which make it problematic as a sport camera.
1) Shutter lag - if I'm reading the specs right, the shutter lag is around 1/2 second. That will make it very difficult to get many shots, such as headers and keepers diving for the ball. Even getting shots of players fighting for the ball will be challenging. Prefocusing brings it down to .015 (which is very good), but it means the AF is dog slow.
2) Frames per second. This camera has 1.4 frames per second. While I'm a firm believer of shooting one frame at a time, the slow fps means that once you push that shutter button, you can't take another image for over a second - likely closer to 2 seconds when focus acquisition is added in. That can be an eternity in sports.
I'd say give it a try with that camera, it will be great practice, but you will have some real equipment limitations.
Well sport photography all ends up boiling down (in my opinion) to two things. Speed of your lens (or in your case camera) and how close you can get to the action from the sidelines. The one and only time I've shot sports (specifically american football), I used my longest lens and I had the sun on my side.
I did a quick google lookup of your camera. According to Nikon, you have about 600mm in your zoom range, which is more than enough for getting close to the action. The real question is speed. I have no experience with a Coolpix, but the basic suggestion would be open up your aperture all the way, and try to shoot with a shutter speed of at least 1/500. So to answer your first question, yes it is technically possible on your current camera
If however, you do wish to upgrade, you will have the advantage of better glass and image sensors on your side. I recommend a Nikon D3200 or a D5100. Both cameras are great entry level SLRs, and I actually shot my only sports photography on a D5100 so I know it's up to the task. You would also need to get a lens that can shoot somewhere in the range of 200mm. Which one I shall leave to your discretion as a camera lens is really versatile so I recommend you choose one suitable to a large slice of your photography needs.
Short answer, either route is possible. Just one will make things slightly easier on you as zooming in and out will be much quicker on an SLR, as will focusing. Hopefully that answers some of your questions. Let me know if you've got any more.