Using AF, Back Button Focusing, and Single Point along with AI Servo is very similar to manual focusing - puts the photograhper back in command - except it's far faster and much more accurate than you or I would ever be able to do consistently with manual focus. Heck, I shot with strictly manual focus gear for more than 20 years... including a lot of sports. Since converting to the Canon system in 2001 and learning to use its AF effectively in various situations, I get a much, much higher percentage of "keepers" than I ever could manage with manual focus.
IMO, learn to use the technology to your advantage... don't just defeat it. Learning Back Button Focusing and Single Point and AI Servo makes all the difference in the world and puts the photographer in charge of AF, rather than leaving it up to the camera to choose.
Also, today's cameras.... especially crop sensor DSLRs... simply are not very manual focus friendly. Smaller viewfinders, no manual focus indicators such as split image and microdiaprism rangefinders, and other factors make manual focus more difficult with a modern camera. With stationary subjects you can switch to Live View, use the rear LCD, focus manually or with contrast detection and zoom in to check focus... and it's highly accurate. But this isn't practical or possible when shooting sports/action. So, again, my vote would be to learn to use the AF system.
I shot a sporting event on Sunday and am post-processing the images right now. As of now I've edited the first 1000, out of around 2700. I always mark my missed focus shots in Lightroom with a "rejected" flag. So far, out of 1000 I've marked two images for missed focus (I've rejected a whole lot more for other reasons... bad timing or closed eyes or lousy composition, poor exposure, etc.). I know there will be a few more and I also recall a couple images that were questionable... focus isn't perfect but is good enough to be usable for smaller prints. I was shooting with a pair of 7Ds - mostly using the simple method I recommended above - and lenses were 24-70/2.8, 70-200/4 IS and 300/4 IS. I wouldn't expect anywhere near such consistent focus accuracy with manual focus, so I generally don't recommend it for sports (I do use MF for other things... landscapes, macro, some portraiture, etc.). But my point is that I challenge anyone to get close to that level of consistency manual focusing. I know I couldn't, and I was **bleep** good and fast with MF.
A key reason I wouldn't use MF shooting a baseball game is that, while it might work okay for the pre-focus situation of the batter at the plate, chances are you're going to see other action around the field and will want to quickly change your point of focus. With the right lenses and AF techniques on 7D, this can be done nearly instantaneously. There is no way you or I could MF fast enough and we also wouldn't have time to switch AF back on. We'd miss a lot of opportunities trying to use MF.
Another consideration... if you are using a zoom, the vast majority today are "varifocal". This means the lens does not maintain focus when the focal length is changed. Back in the good/bad old days of film and manual focus, more zooms were "parfocal" design... maintaining focus when zoomed. But with AF cameras, it's not necessary and varifocal designs are less expensive and easier to correct for higher image quality... might be smaller and lighter, too. So with today's zoom lenses, with any change in focal length you need to refocus. If using AI Servo autofocus, this is happening continuously and automatically. I don't know about you, but when I'm working with a zoom I am constantly changing the focal length and image composition. So this is another reason I'll keep using AF.
