Zooming in tighter would have a bigger effect than using a smaller aperture. Not only would it blur out the background, it would also focus the shot on the subject.
The next thing you need to do is change position. Both of these shots are treating the offensive player as the subject, but shooting the back of his head. In the first shot, you need to be standing exactly on the other side of the shooter. Then you would have a great shot.
In that second shot, if you were around the end line off to your right, you would have got the shooter in profile and you would have the sun at your back making the shadows look a lot better. As it is, any shot where I cannot see the subject's eyes in sports is a shot that goes in the trash bin.
Before shooting any outdoor sports, look at where the sun is and then place yourself for faces, peak action and good light. Then shoot tight and crop tighter. This is why I typically tell people that 200mm is not long enough for field sports, even on 1.6X format. Look back at my examples in this thread and note how tight they are, and how I placed myself for the evening light.
Yes! Location, Location, Location!
I love how much I've learned from these forums. For those of you "in the know" - kudos to you all for sharing and instructing the rest of us on how to get better pictures.
I struggled with lens selection as well - and ended up with the 70-300L. I shoot my kids lacrosse and soccer with it - and am very happy with the lens.
Here's a pic @ f6.3 - but at 300mm . Just using it to show how you get good background blur with increased focal lengths - even when not shooting @ f/2.8 or f/4.
I selected this pic because it's one of the only pictures I've taken at max focal length. My apologies that it's soccer . . .