AF-continuous is a must. 21-points can be helpful if you are not good with tracking. Maybe set Custom Setting a4 (tracking lock-on) to short or off.
Continuous AF happens in two phases. #1 you and the camera need to agree on the subject and the camera needs to lock onto that subject usually by getting a good focus lock using the center focus point of your chosen group. #2 The camera needs to track the subject which requires you to continuously hold the focus button while you keep the subject under the focus points of your chosen group.
This does take practice, but it looks like you have a willing subject.
---------+---------+---------+---------+---------+ Joseph K Seattle, WA, USA