If you're going to track a subject in motion, you need to get two things set correctly in your camera:
Let's get to it in the video:
AF Single: The camera locks onto the subject and STOPS at that point. It does NOT keep tracking the subject if it moves.
AF Continuous/Servo: The camera keeps refocusing continually on the subject. So we'll need to choose this mode for sports!
Wide Area: the camera focuses for you using all of its focusing points. Usually on the subject that's closest to you. The big frustration with using this mode is that a lot of times your camera will choose to focus on a subject that you don't want it to.
Single Point: Only a single AF point is being used to focus. Press your focus button (either back button focus or your shutter...whichever you prefer) and the area directly beneath that single AF point is what is going to snap to focus.
The benefit here: precise control on where your camera focuses.
The drawback here: trying to keep that tiny single AF point over your subject during motion.
Group/Expand Points: The camera uses a main AF Point, surrounded by "helper" AF points which assist the main one, especially for tracking motion.
Okay, that said, let's see this at work in action via another video. This time you'll be looking through my actual lens: