" single point, manual AF selection."
That I would submit, is not the best choice for action work...you're artificially limiting (as in crippling) the camera's ability to do its best job at predictive AF...instead of bringing in multiple data points, you're deliberately limiting the AF system. Try a multi-point AF strategy, I am almost certain you will find it gives better results. 9,11,21 point AF is what I have had best luck with when my subjects are moving. I shoot in AF-C a lot (99% of the time, actually). Different cameras have different multiple point counts, not all have 9 and 11 or 9 or 11. I'm not a fan of using all 51 points.
Admittedly though, the 50/1.8 AF-S is a surprisingly SLOW lens in focus speed for an AF-S lens...it's known to be slow...and compared to the 70-200 VR or 300/2.8 AF-S Mk II, it is slow. But, it's not horrifically slow, but the older 50 1.8 screw-drive focuses faster...I have both, and the G-series 50/1.8 just seems slower than one would expect. I think this might be favoring accuracy and precision, for wide-aperture work. Over the last decade, the 50mm lens has become a favorite of beginning professionals who use it wide-open, or nearly so, at CLOSE distances, as a portrait lens. It's become a very strong trend, and I think there might be a bit of design bias in there favoring high-precision focus, more so than the "speed" focus of older 50's. According to testers who have compared both the 50/1.4 G series model and the 50/1.8 G, the more-expensive f/1.4 model is deemed extremely slow-focusing, but I have not shot that lens, but I've read that multiple times from sources I trust.
But I would ditch the single-point, smack-dab in the middle focusing...a lot of time, with a 50mm lens, that center AF point can be right on the belly area of a person, and on something like a smooth T-shirt, that's really not a very good AF target...adding more AF points gives the computer more data points, and can speed up focusing, especially predictive AF.
In the menus, AF-C also has parameters you can set, giving priority to Release, or to Focus, or a combination of the two. If you favor "Release", that tells the camera to blast away more freely, even if the focus is not dead-dead-dead on; if you're using f/11, there's not nearly the same need to focus critically as if shooting at f/2, and beyond 20 feet with f/11, who cares...you can be off five feet, and DOF will cover it.