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Dr. Chris Yeager is one of the brightest minds looking at the science of hitting. His scientific approach, based on the principles of physics, is detailed in a video he has made available. We spoke to him by phone from his home near the Mississippi Gulf Coast.

Baseball Prospectus: Tell us a little bit about your background and how you came to be a – is the word hitting instructor, hitting philosopher? How do you think of yourself?

Dr. Chris Yeager: I would include both of those. I have coached at the high school level and I also do private instruction. I played college baseball, was a graduate assistant coach at the University of Southern Mississippi, and then coached at two different high schools since then. I finished my Ph.D. at Southern Miss and my study was on the biomechanics of the baseball swing–specifically the effect of the stride and weight shift in the swing. Based on that and my research is where I draw my philosophy and conclusions on how force is produced in the baseball swing.

BP: You produced a video that shows a very different approach to the baseball swing–perhaps not in the way it is successfully executed by someone like Barry Bonds, but different in the way that most people think of hitting. What's different about your approach?

CY: We are really trying to use science, the laws of motion, the laws that Newton came up with, so it's really not new. Sir Isaac Newton came up with the three laws of motion and these cover what would create force not only in a baseball swing, but also in any area of life. I try to use those laws of motion in formulating my theory. I feel like hitting instructors in the past haven't done this. They haven't applied the laws of physics and motion in what they try to teach.

BP: I understand your approach to hitting is very similar to Dr. Mike Marshall's pitching research.

CY: Yes. I know that he does basic teaching on biomechanics and on the laws of motion, which is what we need to draw from if we are going to teach how to properly produce force. We are trying to produce force in the baseball swing and in the pitching motion. If you are going to do those things you need to draw upon the laws that govern motion.

BP: How exactly is force produced through a proper baseball swing?

CY: There are two primary parts of what is called the kinetic link. The kinetic link is what produces force in the baseball swing. The first part is the muscle stretch or 'pre-load.' That's when the baseball player actually lengthens or stretches during his stride. His arms go back, legs stretch, and this gives us what we call eccentric-concentric stretch.

The second part is the conservation of momentum in which the body conserves energy and then transfers it through different body segments. Conservation of momentum is very similar to the cracking of a bullwhip. When you crack a bullwhip you actually bring the whip back and you stop your hand. By stopping your hand the energy created from your body is transferred into the smaller mass of whip. Energy can't be lost; it must be transferred. The whip must gain speed to make up for the lost mass in the system created by stopping the hand and the sequential stopping of each section of the whip. When all but the tip of the whip stops, the transferred energy is concentrated and the tip of that whip actually breaks the sound barrier.

A similar thing happens in a baseball swing. The body creates a forward momentum and is stopped by the front leg. The body then transfers that momentum to the hips, to the shoulders, to the arms, to the hands, and then of course to the bat. Those hitters that do this best–that actually block and transfer energy best–are your most successful hitters, like Barry Bonds and Babe Ruth. This efficient transfer is seen in those hitters who display nearly motionless bodies as the bat approaches contact. The motionless body represents maximum transfer of energy concentrated into the end of the swing, just as one does when transferring energy into a bullwhip by stopping the hand.

BP: We don't think of Babe Ruth in the same way we do modern players but in fact he was unintentionally applying these principles?

CY: All the good hitters unintentionally do it. I don't know that any of them have actually gone in and studied Newton's law and studied the way that energy is transferred by the use of conservation of momentum. The great hitters, the ones that do it well, really show an exemplary job of blocking and transferring energy.

BP: How efficient can the transfer be in a perfect swing?

CY: It can't be 100% but those that allow each body segment to rotate maximally before transferring energy to the next body segment do it best. In other words, allowing the hips to rotate fully before the torso becomes involved, then allowing the shoulders to rotate maximally before the arms become involved. It's about delaying each body segment as much as possible. If forward momentum is not stopped and if body segments turn at the same time, maximal energy transfer will not result. If one were to attempt to crack a whip by rotating in a circle without stopping the hand and therefore not transferring energy, the goal of cracking the whip would not be attained. However, if we stop the whip and then allow the whip to sequentially stop down the line, then we'll get the desired result. The importance of allowing preceding body segments to rotate fully before allowing the following body segments to become involved cannot be overstated.

BP: It seems through your video that the legs and transferring the energy from the legs seems much, much more important to your style of hitting than do the arms.

CY: It's based on the laws of motion. The energy conserved will be moving the body at greater speed than the arms can catch up with. The body should be moving – in elite hitters – upwards of a hundred miles an hour. The muscles of the arms and the wrists do not have the capacity to create speeds of that nature on their own. They're basically along for the ride. All they must do is relax and allow that energy to be transferred. Any help from the hands, because they can't go that fast, will only slow down the bat speed. If you look at the great hitters – Bonds, Gary Sheffield, Chipper Jones, Hank Aaron, or Ruth – you can see how loose the hands were. They do that a lot with a lot of their pre-swing motion to get the hands actually in a position to where they transfer energy at the very end just like the whip does; they lag behind and then transfer energy.

BP: Do you feel like there's any hitting coach today that intentionally or unintentionally is teaching something either identical or similar to your approach?

CY: Not that I know of. Dusty Baker has a book out that has some teachings in there that go against the laws of physics. To be honest with you, I don't know all the theories. I haven't seen them published. I haven't seen them on video. I will say this – I've yet to hear a baseball instructor utilize the laws of physics. There may be some out there doing it. There may be some that don't speak of it in scientific terms because they're afraid of confusing their hitters but they may be aware of them.

BP: On your video, you state that a swing is a swing. Is your approach a better one for a power hitter, an average hitter, or does it apply across the board?

CY: I believe that it applies across the board. I've looked at Tony Gwynn, Wade Boggs – guys that weren't power hitters. Some of the things they did seem to shorten the swing a little bit. They tended to drift a little bit more which allowed their hands to make last-second adjustments. However, I believe that Barry Bonds has perfected it. If you look at him, he's got the strongest block on the front side and he tends to get his hips out in front the best. Of course he strikes out very little. Looking at film, there does seem to be a tendency of singles hitters to drift, to have a weaker block than your power hitters. Ichiro is a great example of that style.

BP: It seems like there are as many different batting stances in baseball as there are players–Barry Bonds has a very neutral stance whereas somebody like Jeff Bagwell has a very extreme stance. Does stance affect your teachings?

CY: Not so much. All those guys are getting their weight back and then they're getting their hips in front of their shoulders and allowing their hands to relax. Bagwell came up with a different way to get that done. He actually strides backwards and then pushes the weight forward to get the hips open that way. Sheffield does a lot of bat wiggling. What that bat wiggling is doing is allowing him to leave the bat behind and to keep it loose like the whip. Bonds does the bat wiggling, where he keeps it loose and leaves it behind. If you look at a guy like a Denny Hocking – off the top of my head – he's a decent hitter but he doesn't extend the lead arm, his hips never get ahead of his hands; they kind of spin all at the same time. He's a decent hitter, but he's never going to be a Hall of Famer.

BP: Mike Marshall has been advocating his approach since the early 70's and has had success at the major league level with it, but his ideas still meet a lot of resistance. Do you feel the established baseball types are going to resist your approach as well?

CY: Oh yeah, definitely, just because I think there's a bit of fear. They've been teaching a certain way and I come in with something new that says that they have been wrong for all these years.

BP: Besides Barry Bonds you named Gary Sheffield and Chipper Jones as examples of good hitters. Who are some players we think of as good hitters that are getting by with a poor approach?

CY: One that I point to in the video is Hank Blalock. He has had some success at the minor league level but at the major league level, he's opening his whole body at the same time and of course he's not allowing his hips to turn fully. I think he's kind of getting by with good hand-eye coordination. Same thing with Travis Lee. Again, decent block on the front side, but doesn't keep the hands lagging far enough behind to reach his full potential. It's amazing when you see the guys that really do a good job of body segment rotation, which starts with the hips rotating first and leaving everything behind, allowing the hands to be loose like the end of that whip. It's amazing how strong the correlation is between those factors and good hitters.

Yeager can be reached at , and he'd be happy to send out his videotape explaining the physics and physiology of the swing and comparisons between hitters.

Will Carroll is an author of Baseball Prospectus. You can contact him by clicking here.

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