There's evidence that juggling and playing tetris increase white matter.

For some reason I found learning to shoot a hockey puck with either hand as the dominant one much easier than trying to do the same for either hitting or throwing a baseball. Throwing a football left handed is even more difficult than the baseball motor skills. Catching a baseball with the right hand was easiest of all to learn (as I learned to catch with my non-dominant hand, as Americans tend to be trained).

There may be a universal hierarchy of the difficulty of these skills, with some easier to start with.