Diving Into First Base: Maybe Not Crazy

“Chester wouldn’t play baseball unless Wilson played, and they never swung at the first pitch or slid headfirst.” — Chester’s Way, by Kevin Henkes

Most of us have been taught that running through the bag is unequivocally faster than diving into it. Those who dive into first base are often ridiculed for doing so, risking injury to themselves while simultaneously making themselves less likely to beat the throw. However, a new way of thinking about the physical effects on the runner as he dives through the bag — pioneered by the father/son duo that make up “Baseball con Ciencia” — shows that the diving runner could close the distance to the first base bag at a faster rate. Theoretically.

Let’s put aside the risk of injury for now. Diving into the first base bag puts appendages at risk that would not having anything to do with running through that same bag. But that’s another topic. For now, we’re just concerned with the physics of it all.

For now, let’s just talk about the dive into the bag in three parts, as Norberto Rivas Sr and Jr have done on their blog.

The Preparation for the Jump
In order to jump down towards the bag, the runner has to get more horizontal. That’s just how it works. Getting horizontal may not seem to be an advantageous thing in itself, but getting there does two things that help. In going towards the earth, your body is allowing gravity to help it lean forward. This stretches out your stride, as well. Here’s what it looks like on a collection of stills from Baseball con Ciencia:

By the calculations of the Rivas duo, this step gives the diver a ten centimeter advantage over the runner. Not large, but it adds up.

The Jump
There are two advantages to jumping.

The first is mechanical or muscular. After preparing to jump, your body is pointed in one direction and the lunge can be one last explosive movement from your legs. In other words, while you are running upright, you’re using your muscles to push both horizontally and vertically. In the dive, you’re doing a squat, and pushing entirely in one direction.

It’s certainly possible that, in some sports, your vertical muscles would be less developed than your horizontal ones. Long distance running, perhaps. But short distance runners and baseball players usually develop both aspects of their muscles, as recent running theory has shown is a smart idea. So if you do squats, that dive can be powerful, as it fully uses one of the largest muscles in your body to push in one direction. You can read a little more about this phenomenon in this excellent post by David Kagan on The Hardball Times.

The second advantage to jumping comes from the fact of flight. You’re no longer connected to the ground, and you are allowing gravity to fuel your flight as you fall closer to the base.

There is some deceleration due to air friction — Physics professor Alan Nathan called air friction’s impact minimal in this situation — but then there’s actually acceleration on the second half of the fall according to Rivas. Rivas explained in an email. “We found a deceleration, as expected, from 9 m/s to 8.35 m/s on the first 1.08 meters of hip flight,” he admitted. “But on the second 1,05 m. of flight, we register an acceleration, passing from 8.35 m/s to 8.68 m/s. This acceleration was limited, because, as soon the hands’ friction with the floor occurs, the deceleration by body/floor friction begins.”

The Rivases estimate that the explosion plus the flight increases the divers’ advantage over the runners by .71m, and made a video showing the difference in controlled conditions — one runner, synched to himself to show the advantage.

They key to maintaining the advantage is technique. According to Rivas, “The average velocity reached by the runner in the last long step is 9.5 m/s. The average velocity of first .6 meter of sliding is 6.2 m/s, and the average velocity of full body sliding was 5.2 m/s.” Since the diver had a .81m headstart at the end of his dive (25.6 inches), it should take much more than a meter (three feet) of sliding for the runner to overtake the diver.

Nathan, when contacted, felt it is possible that, under the right conditions, the diver could beat the runner. He wasn’t sure about Rivas’ explanations, though. “It could be simpler — you’re stretching your hand out, and the extremity of your body is touching the bag before the rest of your body.”

The roles of gravity and air friction might be overrated in this analysis, he felt, but he did admit that gravity would give your body an assist by “helping to provide the torque” necessary in getting into a diving position. That links up at least generally with what the Rivases say about the benefits of the diving position above. If your technique is right, gravity helps your body along.

But really, the whole advantage gained throughout the dive depends on technique, according to the Rivas family. Their main critiques of the ESPN Sports Science takedown of diving had to do with two points.

One, they felt that Sports Science didn’t make sure that the two runners being compared were at the same velocity going into the slide, which might be a matter of science or technique.

Two, they felt that the example runner did not make enough of the muscular advantage gained by lunging. You’ll see Barry Larkin and Harold Reynolds discuss some of the proper technique of running into a dive into first here. They even mention the aspect of keeping the sliding distance short. Rivas feels that the proper technique has a runner beginning the process at 23 feet, diving at 13 feet, and sliding about a foot or less to the bag.

And, let’s return to the injury factor that we left alone at the beginning of this piece. Even if Nathan believed it was possible for the diver to beat the runner, he thought it was a dangerous activity, particularly since he felt the runner should literally be diving straight for the bag.

Rivas once again felt that technique was the answer here, too. He pointed out that Brett Gardner does a great job of sliding on his wrists, not his palms, so that he can keep his fingers up, and included a still of Gardner sliding as a reference point.

In the opinion of Rivas, the action is low risk with the right approach. But it does seem like a lot of this hangs on technique. You certainly wouldn’t want your Josh Hamiltons sliding into first base regularly; that’s an easy way to get hurt.

But your Brett Gardners? They are used to sliding head first, and they know how to use their last explosive movement going into the slide correctly. They might actually get an advantage from diving into that first base bag. At the very least, it might not slow them down enough to be worth all the outrage.