IMHO, I think you've got some real issues with your technique, Schnur.
In your first photo, you've got your focus on the player in the foreground with their back turned to you, instead of the ball kicker. In the second shot, the focus is this time well behind the action - look at how much sharper the players walking at the back are!
If you haven't done much sports shooting, you've got to practise locking focus on a player before you intend to take the shot (listen for the beep!), then use your panning skills to smoothly keep the point on them - watch a good TV coverage cameraman. If you stray off the target, start again, including waiting for the beep.
An issue with team sports is players moving across in front or near your intended target. This is why I won't use 'Auto' for such situations. On the K-1 or K-3 you can choose to adjust the tracking ability to make the camera ignore something temporarily closer to the camera. The K-30 doesn't have that setting but it's still possible to use the back-button focus method to minimize this happening - disengage anytime a distraction is going to happen. Your sense of the game will tell you that when the ball is fairly stagnant in the middle of a cluster of players, this is going to happen a lot, but when it comes out and a forward is one-on-one with defenders in open space you can get fantastic shots, click that button a lot!
When the ball is in congestion, don't be afraid to sense the opportunity for a quick manual focus shot too to get some beautiful subject isolation. Remember, it's the faces you're after, not the actual ball, which moves a lot quicker and more randomly. You are really doing portrait photography at 1/1000s, and remember all the lighting principles are the same.
I shot runners in AF-C no problem with your lens the other day on the K-1 at f4, which is similar to the f2.8 DoF on your K-30.
Your pics are always worth the effort if your kids or friends are involved, and you can achieve what's simply not possible by the other parents with their phones, so best of luck with your practice!