Everyone has a different style, although it seems that most will use AV with a wide aperture (Low f-stop) and adjust the iso as needed to keep shutter speeds high. There are plenty of people who will also tell you that "you can freeze action at insert incredibly slow shutter speed here, but I have found that 1/500 is a minimum, and if there is enough light, I would prefer something faster- 1/1000 works great.
Manual, AV, TV, "action mode"..... The important thing is that you get to the settings you want, not how you get there. Keep experimenting, and find your style.
For me- in this circumstance, I would have used AV. A setting sun means changing light, and I would rather have the camera making that adjustment than me. Your first shot is in mostly shade, your second in full sun. As the sun sets, things get darker. Changing manual exposure in that circumstance is possible, but excessive in my mind. If the sun set all the way and the lights come on, now you would have more predictable lights and I would switch to M. Had it been earlier, and the light on the field was consistent, M would be a good choice there also.
Don't get frustrated- there is lots to learn! Once you have the camera set up to your liking, you will want to be concerned about focus points, modes, and white balance. There is always something that can get better!
