Spin Rate: Batted Balls Missing Component by Jeff Zimmerman January 9, 2018 Quite a bit has been written about batted ball data the past few seasons since the information has become publicly available. Fantasy owners have taken notice and are trying to find that next hitter who is raising his launch angle to be part of the “Flyball Revolution”. One major issue which is not being publicly discussed is the major effects backspin has on the ball. By knowing a hit’s spin rate, some of the anomalies seen between launch angle and exit velocity can be explained. The spin rate is a major batted ball component but is generally an unknown factor. The importance of batted ball spin comes down to this simple table and explanation by Dr. Alan Nathan in a piece he wrote at the Hardball Times. Finally, I want to take advantage of the fact that we have an aerodynamic model that accounts for most of the features of the data to investigate how flyball distance depends on the amount of backspin, here for a fixed exit speed of 103 mph and launch angle of 27 degrees. The results are given in the table below. They show that distance increases rapidly as the backspin increases from zero but eventually saturates, with very little gain in distance for spin rates exceeding about 1,500 rpm. The reason for the saturation is partly because air drag increases with increasing spin, essentially canceling the increase in lift. Same launch angle. Same exit velocity. And the ball travels an additional 64 feet of distance because of backspin. Simply, how is a factor which can add an additional 60+ feet in travel distance not be part of our analysis? Backspin isn’t everything. The hitter needs to be able to hit the ball at 103 mph and 27 degrees in the above example. But just a small bit of offset can make the difference from a 336-foot flyout or a home run. The problem with spin is there is no data to actually analyze. With no spin data to use, all the following pieces of information are based on a heavy dose of theory and almost all taken from the work of the great Dr. Alan Nathan. I had to correspond with him to help navigate several of his academic papers and can’t thank him enough for the help he provided. For those wanting to start understanding the effects of batted ball spin, start with his article Optimizing the Swing. Here is his explanation of how backspin in generated: Suppose a ball is hit off a tee, so that there is zero pitch speed and spin. Suppose further that the offset and attack angle are adjusted by the batter so that the attack angle of the bat is right along the center line. Under such conditions, there is no sliding and, therefore, no friction, and the ball will exit along the center line with zero spin. If the attack angle falls below the center line, the friction will be down and to the right on the diagram, so that the ball will exit the bat with backspin and in a direction below the center line. Similarly, if the attack angle falls above the center line, the ball will exit with topspin and above the center line. And for a visual on the batted ball offset, which generates backspin, here is a simple diagram: Generating backspin does come at a cost of exit velocity as seen in these charts for the same article and the conclusions Dr. Nathan drew from them. The top plot shows exit speed versus offset and demonstrates that a high exit speed can be achieved with a wide range of offsets. The middle plot shows that maximum distance is achieved with an offset around one inch. That would be the hitting strategy if the goal is to hit a home run. The bottom plot shows that short hang time (along with high exit speed) is achieved with offsets less than 0.5 inch. In effect, this type of hit is a hard-hit line drive with a low launch angle, leading to a safe hit with high probability. These plots demonstrate quantitatively what most people already realize. Namely, that the two different goals (home runs versus on base) require two different hitting strategies. Without the actual spin numbers, a proxy can be created for them. Since spin is created by offset, the average offset needs to be calculated. It starts with the attack angle (or swing path) the hitter takes at the ball. To start the discussion, I will point you to Jim Albert’s work at Exploring Baseball Data with R. While I recommend the entire article, scroll down to the “Looking Further” section with the Exit Velocity versus Launch Angle graph. Every hitter, with enough batted balls, will create a similar plotted graph with a curved top. The launch angle value at the peak velocity is the attack angle (shown in the earlier image of batted ball collision) or swing path. It’s the launch angle which will generate the hitter’s highest exit velocity. These batted balls have no spin and won’t travel as far as those with spin. Here is a similar graph Note: I was unable to contact Jim Albert for permission to use his images so here is an example from David Marshall in our Community Blog. Albert points out Miguel Cabrera had bad luck on some of his batted balls. Compared to the norm, more were turned into outs than expected. If the spin values were available, Albert could find out that the non-hits may not have had enough spin to go the needed distance for extra-base hits. The general public is left in the dark about spin rates but we can slog ahead. It’s time to move onto the work of David Marshall in our Community blog (thanks for the image above). He wrote a must-read article for those attempting to understand this subject and created this outstanding graph. It shows the hitter’s calculated attack angle (full list of attack angles) and the actual launch angle. The difference between the two angles should be the average offset angle (spin proxy) for the hitter. Other factors come into play but this value gives users an idea of the backspin the hitter is trying to create against the average pitch. Going back to Dr. Nathan’s work, he stated that 0.5 to 1.0 inches is the desired offset but his data is in distance, not in angles. *** Warning: This data could be wrong and needs to be verified, probably a couple times over. *** I broke out some my high school trigonometry knowledge and calculated the ideal “launch angle – attack angle” to get the best offset angle using the batted ball offset image. I’m not going to show my exact math now but would like someone(s) to do the calculations independently. For reference, here are the angles I have for various offsets. Offset Distance (inches): Offset Angle (deg.) 0: 0 (One is right) 0.5: 10.5 1.0: 20.7 If (big IF), my calculations are correct, hitters should be looking to have their offset angle between 0 and 21 degrees. I would argue that they may try for 10 degrees and if they are off, they move towards their maximum exit velocity at zero degrees or the other way towards their maximum distance at 21 degrees. Again, if my numbers are correct. Before moving onto making further observations, I want to make sure my assumptions and math is correct. I hope everyone stayed with me. Now that I’ve gone over a bunch of batted ball spin information and how it may be messing up our analysis, here are two additional facts to consider when looking at batted balls. Slip The higher the offset between bat and ball, the more spin, up to a point, is generated. If the offset is too much, the ball slips and then bounces off (i.e. balls fouled up straight back). In an academic paper, Dr. Nathan and others published the following: Normal batted ball collisions break down at 40 degrees. For people doing research, they may want to group all these high-angle batted balls together because they no longer act like the rest of batted balls. From 2015 to 2017, the average wOBA on balls hit at 40 degrees or more was just 0.038. Not good. I could just find one reference to this idea and it could be a great focus for a future study. Increased Bat Speed and Mass Equals Less Offset for the Same Exit Spin Originally, I got this idea from someone reaching out to me to see if I had seen any research on bat speed and spin. Their data pointed to more spin at higher bat speeds. They just wanted to make sure nothing was off with their numbers. So here is the equation which explains it all. And I was lost also. Most of the variables are constants like the construction of the ball or the offset (Sin U). The key factors to consider are: w = Spin Vbat = Velocity of bat Rx = Bat construction and recoil factors Figuring out how much each variable needs to increase to get the same spin rate is beyond me. I can determine that a higher bat velocity component will increase the final spin if the other variables remain the same. So, if a hitter has more bat speed, they won’t need as much offset for the same desired spin. And because they don’t need as much offset, more energy can be transferred to the ball in the form of exit velocity. And there is the “bat composite” component which I know matters but not sure how and by how much. Sorry. Conclusion Not everyone is ignoring batted ball spin. Major league teams are utilizing batted ball spin rate. Additionally, I know of a couple colleges who are using the spin data they have collected to help work with their hitters. Anyone who has the information has found it useful. Before the batted ball data was available in 2015, the public was operating on the pitching equivalent of ERA. Fans knew the end results but were not sure the inputs.Researchers determined strikeouts, walks, and some measure of batted ball data (e.g. home runs or flyballs) make up most of what affects ERA. It had three components. With the batted ball data, we have two known components, exit velocity and launch angle. Now some decent conclusions can be drawn from the two data points. Without spin, it’s like saying walks and strikeouts are all that matter without even knowing what happens once the ball is in play. Ball-in-play results add needed context to ERA estimators, spin needs to be included in batted ball data. Until spin is available, results will be suspect since batted balls with the same exit velocity and launch angle may differ in distance traveled by 60 feet or even more. We have no way to know. Users who have spin data are making major advances as the general public lags behind. Even without actual spin rates, a proxy value can be created using calculated attack angles and actual launch angles. While not perfect, the values do provide some insight into how hitters are attacking pitches. While the key for many field experts is to encourage hitters to elevate for better results, elevating isn’t the only factor. A little spin-generating batted ball offset could lead to as big of a change. The world of batted ball data is just being scratched and hopefully, everyone can have a better understanding of batted balls and their eventual results.