When I was shooting soccer, I found my best bet for action shots was to just follow the ball. It was relatively large, with good contrast, and moving at a rate I could follow with a long lens.
I quickly found that the same tactics didn’t work well for baseball. It was much smaller and faster with no high-contrast markings. When I tried to follow a line drive or even a pop-fly from the edge of the field, I seldom had time to focus on the fielder before the ball disappeared into his glove. Once that ball was swallowed by the glove, the shot wasn’t really worth much visually. Or even worse, the ball would never make it into the glove, sending the fielder scrambling. This might be an okay shot for a photojournalist sending pictures to illustrate a disappointing loss of the home team, but if you are taking pictures of players for their scrapbooks, it’s not a moment you want to immortalize.
I found more success when I watched the players instead of the ball. Leaving my lens zoomed in, and both eyes open, I follow the gaze of the infielders and then the outfielders who are all watching the ball for me, until they lead me to the player whose body language clearly indicates that this ball is his. In the case of a long pop fly, I may even have a second or two to focus on the player and take multiple shots as the ball drops toward his outstretched glove. This gives me a few usable action shots even if the ball never lands neatly in the glove. In fact, the approach shots are usually more compelling than the shots of the completed catch, since the ball is still clearly visible.