Looking at this Mike carefully shows that the eyes , nose and mouth area are out of focus while the top of the head is sharper.
The use of f2.8 has restricted your D.OF. At this wide aperture the focus point is very critical
as there is little d.o.f . and even a small distance can make a difference to the sharpness of the eyes nose etc.
Trying f4 or f5.6 would give more latitude in focusing while keeping the background still out of focus. However at 4 or 5.6 your shutter speed would be slower so you could nudge up the iso to compensate.
Also I notice you have ev set to -O.7 you would probably get away with -0.3 , this would help with shutter speed.
I know it is a VR lens but a monopod would have really helped here with stability, yet allowing you to retain flexibility of following the action.
Your lens can be used confidentally at f2.8, it is designed that way and is why you paid a shed load of dosh for that confidence, however technique is all and once mastered you will be amazed at what it can give you,
Wish Santa had brought me one!!