|Brandon Phillips, second baseman|
of the Cincinnati Reds, juggles
a ball during a Friday workout.
I doubt such activities are a formal part of any team's practices, but such displays of manual dexterity aren't uncommon and may even be useful for middle infielders.
Phillips, as a second baseman, is frequently called upon to make rapid-fire catch-and-throws, particularly on the double play pivot. Part of that is "grabbing seams" — gripping the ball with the fingers of the throwing hand crossing the seam of the ball. This is essential to making a true and accurate throw.
Phillips may be just fooling around here. But he may also, intentionally or otherwise, be drilling himself in the muscle memory that can turn a misplay into a good play.