http://www.flickr.com/photos/jmimage...7622593973053/
In the first one, you need to crop off the top and bottom. Get much tighter. It doesn't have to be 4x6. It also looks a little soft.
http://www.flickr.com/photos/jmimage...7622593973053/
Second one: good capture. I like it. Well cropped, good catch on the action. Wish we had a little room on the left, so that his cleats were completely in the frame.
http://www.flickr.com/photos/jmimage...7622593973053/
Third one with three problems. Soft, not cropped tight and you are looking at their backs. Great timing with the ball in hands in the jump, but you want to see eyes.
http://www.flickr.com/photos/jmimage...7622593973053/
Again, crop tighter and the pic looks a little soft. Again, good timing and composition.
http://www.flickr.com/photos/jmimage...7622593973053/
Fifth: Good timing again, but you can't see a face or the ball. The ideal spot would probably be on the 20yard line, so you are looking right at the ball carrier's face. Just the luck of the draw on some plays. I want to see the eyes and the ball on pretty much every shot.
http://www.flickr.com/photos/jmimage...7622593973053/
6: Looks sharp. But you can't really see what's happening. Feet are cropped off. Try to get lower. Unfortunately for the big uglies, no one cars about pictures of the blockers or linemen. They want pictures of tackles, rushes, throws and catches. And people flying.
http://www.flickr.com/photos/jmimage...7622593973053/
7: Nice and sharp. But watch your horizon and crop tightly. You only need the ball carrier and number 6 who is on the ground. Everything else is distracting.
http://www.flickr.com/photos/jmimage...7622593973053/
8: The defender is too far from the ball carrier. Crop it to be an isolation of the ball carrier and straighten the horizon. Bring a little light into his face mask.
http://www.flickr.com/photos/jmimage...7622593973053/
9: Boring shot. Nothing is happening. Skip it. The only person who wants to see it is the holder's mom.
http://www.flickr.com/photos/jmimage...7622593973053/
10: Again, nothing is happening. You are cutting the linemen in half. For a shot like this, you need more interesting foreground things, background things or for the QB to be doing something interesting. If he is waving his arms around while the linemen are down, it can make for an interesting pic. Him just looking up doesn't really do anything for me. Doesn't tell me a thing.
http://www.flickr.com/photos/jmimage...7622593973053/
11: Good capture. Get a little lower to get under his facemask. Crop tighter. Get rid of everything left of the ball carrier and most of the turf.
http://www.flickr.com/photos/jmimage...7622593973053/
12: I want to see his face. Get downfield and shoot back at him.
http://www.flickr.com/photos/jmimage...7622593973053/
13: Good timing again, but you can't see their faces. It has to be an exceptional picture for it to be great without seeing their face. Your horizon is a little off.
http://www.flickr.com/photos/jmimage...7622593973053/
14: Looks good. Horizon is a little off and the defender is a little too far away. Use a wider aperture to blue out the background.
http://www.flickr.com/photos/jmimage...7622593973053/
15: Good shot. Getting the emotion on the sideline is very important. But be careful of the background. You want it as clean as possible. If you had rotated a little left, you could have gotten his second head out of the picture.
http://www.flickr.com/photos/jmimage...7622593973053/
16: Again, you want faces. Even if the faces are boring, they tell more than backs. Your horizon is a little off.
Overall, pretty good work. Your timing on a lot of those is excellent. Use a wider aperture to better isolate your subject from your background. Mind your horizons. Check your backgrounds and try to get them as clutter free as possible.