I was a thrower on the track team in college (hammer and 35 lb weight), so we threw things, lifted weights, then watched video of us throwing the things, did dry runs of our footwork without the implements, and did visualization exercises running through our form in our head (and targeting a personal record, because as long as you're there you might as well). With a sport where there are a lot of discrete parts to the movement it's hard to think about things like where your weight is at each chunk while you're going full speed. So breaking it down on video in slow motion helps you see what you are physically doing, the dry runs let you focus on each step, and the visualization is important for putting it together in your mind before you go and try to replicate at full speed. For some sports like weight lifting there is a really big mental barrier to break in order to set a personal record, someone can be stuck at a given maximum lift for years, so for them the visualization can be much more about erasing that barrier before they try a heavier weight. A baseball swing is probably a lot closer to throwing a hammer or discus than the weight lifting end of the spectrum.