This is horrible. First off, I earlier explained that friction (at least from the ground) is not in play here. You are diving to touch the bag immediately, not to slide into it. Second...the bold part. A science teacher's head might explode if a student told him this with no explanation. No, you just explained why when you stop running you don't necessarily decelerate. F=ma. There is air-resistance...but that effects you when you are running, too. In fact, continuing to run will INCREASE the frictional forces working against you as you are still connecting with the ground. I'll conceed the point that not taking those last two steps will decrease your speed as you cross the bag. I am not arguing that and never will. But the advantage of being able to reach out and touch the bag as your center of mass is significantly behind the bag offsets that slight loss of speed. if you slide, foot first, into the bag trying to time it so you don't actually slide on the ground, i guarantee that your foot will no longer be attached to your ankle about 0.03 seconds later Great, while you test that, I'll dive in head first, since that will be faster anyways. have fun breaking your finger/dislocating your shoulder when you run into the first baseman's leg