I've taken action photos of professional sports like water polo, rugby, soccer, football, and basketball. Being a sports fan, I love being a part of the action and the camera has allowed me to do that. Thankfully I have a daughter who loves sports which gives me an opportunity to photograph her and her teammates. Sharing the images with the other parents is really gratifying. And it beats having to fight the deadlines.
In all these sports, the best advise I can give is get on the level of the athlete. I see too many parents shooting from the stands. The action is in the eyes, expressions, and physical movements the athletes create. If you are positioned above the subject you miss all three elements. Get on the deck, grab a chair and shoot. Don't worry about ho many pictures you are taking. Anticipate the movement of the ball and fire off 5- 10 frames at a time. The 5th or 6th frame will be the best ones from each sequence.
Another essential element is the zoom. You want to be able to isolate the athlete as much as possible. I have used both the Canon 70-200 IS 2.8 L Mk2 and their 300mm f2.8. Both are amazing, but for sharp images the 300 is spectacular. I avoid having to post edit crop- with so many images get it right in the camera. Fill the frame and fire away.
Finally, a fast enough shutter to freeze the action is a must. This can be tricky in low light gyms. But with the 5D Mk3s I can shoot comfortably with an ISO at 20,000 and not worry about the noise. This has been a huge game changer. To freeze the athlete, I try and maintain a 1/500 or faster shoot at f 2.8-3.2. With an L lens, wide open is still amazing.
Canon 5D Mk 2
Canon 70-200 IS 2.8 Mk2