While looking at my future needs for possible sports photography, I analysed the actual needs of each type of sport and the techniques required.
Longer lenses allow for better focus as the subject moves less in relation to you. If shooting length ways down the ground, with decent depth of field, the single shot or continuous AF of even the EM5 mk1 will get the job done. If trying to follow action from the side, manual zone focus and timing will get good results.
Swimming and distant athletics.
This is the one I did recently that started the madness. Manual zone focus will get diving in, the lanes guarantee the same plane of focus from the side and focussing on the "bow wave" of the subject will work for single or continuous AF for converging targets.
Short distance sprinting.
This is the tough one. How I used to do it was to focus on the runner about to leave the blocks (from the finishing end), shift focus once or twice down the track getting the subject with a short burst as they pass through the focus point and then settle focus on the finish line, usually zoomed right back (this can be achieved by memorising finger placement at each of the focus points). Using the most depth of field possible and with a bit of practice, a set of 10 or so good images out of 15-20 is the norm, including zooming. If shooting from the side, practice panning with good depth and a slowish shutter speed, the longer the lens, the longer the focus sweet spot holds. The long lens trick I learned photographing dragonflies in flight (remember to keep one eye on the action and the other on the eye piece).
Tennis and Netball.
I used to shoot a lot of Netball and found that the field sport techniques worked (shooting long down the length or zone focus from the side), but you also have the opportunity to do some high or low wide angle and short lens work around the goals or base line in tennis.
The trick is to be smooth and gentle with focus, no jerky movements and trust to depth of field if available. Single shot AF is ok as long as the total process of focus and fire is not slower than the subjects movement. Practice on moving cars is good to. Shoot wider than needed as 16-20mp has plenty of cropping power for web work.