American football it one of the most difficult sports to shoot in my opinion, especially if its the senior game you cover (11 v 11). There are a lot of bodies which often get in the way, it's difficult to follow unless you know the game well (will they run or pass for example) and happens in short bursts so by the time you know whats happening it's over. There are a few things to think on for the next time you are out.
1 & 2 - The focus is on the wrong player, the player in the foreground is in focus when it should be the ball carrier. I don't know if you've cropped in on this photo but if so try and avoid cutting off limbs of the key subjects (tackler in foreground in this instance). I know it's very difficult to do so and I've done it with players in the background, but never for the key subjects of the photo if I can help it. The photo is also overexposed, either adjust in camera (best option) or in post.
3 - Personal preference but I would have given a bit more space in the frame on the left, showing what the player was running into, even if it's empty space. I don't mind the cutting off the limbs of the player in the background (although again, avoid if possible)
4 - This is good, only issue is that it could do with some straightening as the horizon is not level and maybe a tweak on the contrast to pop the colours a bit....the last one is a personal preference.
For a first effort though, good work.