Tim, great effort. Glad you had fun. I'd work on your composition, cropping, and understanding of peak action. Here are a couple examples.
#1 has too much dead space above and a lineman's leg in the shot. It's also non-peak action. Peak action would be the moment the qb releases the ball.
#18 is kind of the same. Can't see his face and his body motion isn't dynamic or peak action.
#9 and pictures from the same sequence don't do anything for me. I can't see a ball, and I can't see a face.
#20 isn't the best angle or the best frame. He's flat footed which makes the image static and I wish he were coming at me more. The ref muddles the background too.
From an approach standpoint I'd like to see tighter shooting. Maybe rent some longer glass or simply get closer to the action, if possible. Did you try moving around the field or were you staying in the endzone? I like shooting 10-15 yards behind the line of scrimmage a lot of times. This way you can get the faces of tacklers as well as receivers coming back on a hitch route about to catch the ball. Inside 20 on the sidelines is also a nice change of pace.
Great composition on #6 and nice bokeh on #17. I enjoyed those frames a lot. Hope that helps. Keep up the good work.