biggerpapi
Often this is done when the runner is taking a one way lead. The one way being back to 1B. It is used to draw a throw. From the pitchers view it appears the runner is leading off farther than he really is. Sometimes you will see runners reacting back to 1B while the pitcher is going to the plate. Typically this is used most often by teams that run a lot. Used to get a read on pitchers move. Getting picked off while taking a one way lead is a sin! It is a crossover and dive back to the bag. The crossover happens with any indication or movement by the pitcher. Thus the runner taking the cross over back to the bag sometimes when the pitch is going to the plate.
There are a few other reasons (situations) for leading off 1B like that, but I think it is done most often for the reason above. Anyway, that was the main reason we used it. That said, I don't really know why the team your watching is doing it.