I didn't notice it too much with the shots of just players on their own out on the field but when the background behind them was in the framing it becomes more evident. Really hope the R7 MkII will have this issue resolved!
I noticed the rolling shutter effect early on when shooting a squirrel that was just sitting there. I was shooting in burst mode. The camera moved slightly between frames. That changed the shape of the squirrel slightly. It was pretty obvious when viewing the images alternately. After that I went to first curtain and no more problems with rolling shutter.