The image you posted the link to is in bright sun, the first thing I thought was you were not using the lens hood which would allow reflections in the lens from off axis strong light sources.
Then I saw the image data and noticed the exposure aperture as f/1.8! that is allowing a lot of light in for which you needed very fast shutter speeds to expose. The lens is being saturated with light at f/1.8 and if no hood is used, I would expect more reflections than you are getting. Return to normal ratios of the exposure triad and I bet it disappears.....and use the hood, that is what it is for.
You were in Aperture Priority mode, so all you need to do is set it to f/8 and your would get sharper images with better color at those actions speeds and light level.
When deciding on an exposure mode, determine what element of the exposure triad is most critical for the shot. In this case it is the shutter speed since there is action. Then how fast is the action, moderate in this case, setting Shutter Priority to 1/1000 would safely freeze the action and and let the camera determine aperture. If you use Auto ISO, set the range limits but better, use fixed ISO based on the lowest needed for the conditions of light. in this case ISO 100 or 200 would assure the sharpest, least noisy images since you have lots of light. The variable left to the camera is only one, aperture. In any photo condition you will find 1, possibly two variables important to the exposure quality, and it becomes more critical of a decision the lower the light or the faster the subject.
Is there a possibility that you were using Live View? Light entering the View Finder can create those reflections also.