I have an age old question. I have been teaching my high school aged players to round the bases touching the inside corner with their LEFT foot. I was taught to use the left foot as a child, I have read that one should use the left foot, but I have trouble answering the “why” question. Why should baserunners touch the bases with their left foot?
Coach Swift answers:
The reason is relatively simple, though I will admit when you’re learning to hit the inside of the bag with your left foot it can seem awkward, but it is correct.

As we approach each base, at about 10 feet out we have to make a small arc so that we are approaching the bag at an angle instead of straight on. The reason we round it with our left foot is that we lean to the left while the right foot does the crossover step to start toward the next base. It’s all in the physics: when the foot strikes the bag it starts to slow us down, but if we lean to the left we are hitting the base, crossing our right foot over, and driving through the bag with our arms. The centrifugal force will keep the momentum we have and not cause us to break stride.

If we hit a base with our right foot, we lose some of the momentum built up running to the bag. It’s really key that the runner creates a little bit of an angle when approaching the bag and tries to run hard, not slowing down. It’s one of the small intricacies of baserunning that some players never really learn. It’s not the worst thing to do incorrectly, but given a choice it’s easy to do it right.

Also, to keep players from over-running second or third base, teach them to put their foot on the bag and at the same time drop their butt just a little bit. This action will take runners from full speed to zero speed immediately.