We photographers are going to need two things a camera and a lens and probably a flash. First we need a camera. When deciding on a camera focus speed, frames per second, and high ISO performance are major considerations. To shoot football I use a 1D Mark II. It is an 8 MP camera, and shoots 8.5 frames a second. It focuses like lighting and holds its focus on moving athletes. It is no longer in production. THere are several others out there though from $800 to $5000.
Next a lens is needed. I shoot football and fastpitch with a 70-200 2.8 lens. It is a fantastic lens that focuses faster than the speed of light, and provides excellent image quality. Today it costs today around $1100, the F-4 version can be had for around $650, and both are excellent lenses. There are a lot of other lenses out there. Too many for me to provide a evaluation of each. If you want opinions then let me know.
The last thing is a light system. Most of high school football is played at night, and I know it looks like there is a lot of light. There isn't. Oh some of you may be lucky, but most are not going to be. For us as photographers that means high ISO and shallow depth of field. I shoot at ISO 800 and at an F-stop of 2.8, and even with those settings I use a flash. Now, some new cameras have a useable ISO a lot higher. With one of those you may be lucky enough to obtain 1/500 of a second shutter speed (1/500 is the speed I feel is needed for sports) and not need a flash. Or you may find me wrong and go ahead and shoot with a slower shutter speed. If you need a flash though there are more problems.
In a previous post( http://grangerphotography.blogspot.com/2011/04/light-outside-camera.html ) I discussed the different types of flash. A flash gun will be most successful shooting football. An on board flash has serious limitations. Usually the flash is not very powerful, sucks the camera battery dry much faster, and takes a long time to recycle. In the earlier post I provided some examples showing the lack of power with most on board flashes. Since the flash uses the camera batteries you might not have enough juice to shoot the whole game. I hope your athlete doesn't do something spectacular after it quits. In addition they take a long time to recycle. Recycling is the length of time it takes from the flash firing to the time it is ready to fire again. With an on board flash this can take several seconds. You will only get one shot per play. You might as well leave it at home and have good time at the game.
Another consideration is flash sync. THis is the fastest shutter speed your flash will allow you to achieve without part of the photograph being totally black. With most cameras this will be from 1/100th to 1/200th of a second, but some are at 1/30th. The good news is the flash freezes motion. For football I use a camera that syncs at 1/250. Motion blur (pic below) can still be a problem.
Flash guns are a different story. THey have enough power, they don't use the camera battery, and they have a faster recycle time. Oh we are excited now. Now comes the bad stuff. They have a faster recycle time, but the most you'll get is two shots. They still go through AA batteries like nobody's business. So how do we solve this latest dilemma? A battery pack. Mine cost $150.00. It lasts about a year, and then another one. It also requires a wire $250, $400 total. What do you get for this? Three shots a play, and sometimes four.
Of course none of this makes any difference if you shoot during the day.
Boy I'm glad the ref's pants didn't split. I'll bet he is too. Oh by the way he scored on the play, and it is 11 pics.
So now you have the camera, lens, and lighting system (if needed). Your at the game and ready to shoot. Not yet, first you should get clearance with the Athletic director, or the organizer of the event before going to the sidelines. Then you are ready, but be careful. I have been tackled, and while holding about $6000 worth of equipment.