There are a few features that make a camera especially well-suited for capturing sports and other challenging action.
A fast frame rate is one such feature. A camera that can capture images in rapid succession is more likely to capture the perfect subject position than a camera that captures images at low frequency. For this feature, the EOS R has a relatively fast frame rate, but only when not tracking and adjusting the focus distance. Not all action involves changing focus distances (such as the wave crashing example in the Canon EOS R review), but if your subject is moving enough to leave the camera's initially-focused depth of field, as is typical for many sports, continuous focusing is required and in that focus mode, the EOS R's 5 fps frame rate is on the slow side of the spectrum.
Another feature required for photographing subjects in motion is maintaining a continuous view of that subject in the viewfinder. Optical viewfinders have a short blackout period for each image captured (while the mirror is raised) and cameras with short blackout specs are more-highly desired than those with long ones. Electronic viewfinders, with few exceptions, have a pause in the EVF video feed as each image is captured and the duration of this pause can hinder a photographer from keeping a subject properly framed. This pause is only a minor issue for subjects moving directly toward or away from the camera, but keeping subjects properly-framed as they are moving from side-to-side or moving erratically becomes a challenge with most EVFs, including the EOS R's.
If the subject focusing distance is changing, especially if it is changing rapidly, autofocus tracking and prediction performance becomes critically important. If the subject is out of focus, the image, regardless of the frame rate it was captured at, is likely going to be deleted.
The Canon EF 70-200mm f/2.8L IS II USM Lens and its just-introduced replacement, the Canon EF 70-200mm f/2.8L IS III USM Lens are ultra-popular sports lenses and I mounted one on the EOS R to photograph a cross country meet with. While this lens is not going to create the focus challenge that, for example, the Canon EF 400mm f/2.8L IS II USM Lens will when compared at the same distance, focusing on a very close and fast-approaching runner at 200mm f/2.8 is quite challenging to an AF system. I thought the EOS R did a great job on this cloudy day that included some light rain earlier in the meet. A high percentage of my images were sharp (when I kept the subject properly framed).
Note that, while the image shared here appears very sharp at this resolution, my 1/1250 shutter speed was not quite fast enough to stop the lateral motion at this distance. Though the image is properly focused, the motion blur degraded image sharpness slightly at full resolution. I was starting a burst capture when the subjects came close to being ideally framed and continued to photograph until they passed by.
Another feature that is often helpful for action photography is the ability to sustain the frame rate for a large number of images. The EOS R's buffer depth, when using a fast memory card, is very good, allowing a relatively long period of action to be captured. While usually not as desirable as a fast frame rate, a large buffer can increase the number of great shots captured in a burst and I can credit the image shared here to that feature.
For those using the shutter release to time their captures or to time the first capture in a high speed frame rate sequence, a short shutter lag is important. The EOS R checks that box and the fast AF makes timing single shots quite successful.
Overall, the EOS R is lacking a few key features to make it the ideal sports and action camera. It is not that camera, but it can certainly do that job if needed. I don't recommend purchasing an EOS R for dedicated sports and action photography, but the EOS R stands ready to fill in for the occasional action needs it encounters. Of course, if your action is not leaving the established depth of field, the EOS R can do 8 frames per second and that rate is quite fast, making it suitable for such needs.