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What Makes A Baseball Bat Illegal?

People actively involved in sports are always looking for something that will give them an edge over the competition. Baseball is no different, and the most common place where an advantage is desired is the baseball bat. If a baseball bat is modified in any way to give a hitter an advantage, it may be considered an illegal bat.

Nine wood baseball bats laying next to each other in grass

Because the rules around bat modifications can vary from league to league, a lot of people wonder what makes a baseball illegal. I found myself wondering the same thing so I decided to do some research on what makes an illegal baseball bat.

Generally, any tampering that changes the original specifications of the baseball bat will cause the bat to be illegal for any baseball league. Illegal tampering includes adjusting the bat’s weight, length, or surface area. Certain levels of the game also have bat specifications that must be adhered to.

Making modifications to a baseball bat can give you an advantage during any at-bat, but certain modifications will make the bat illegal. There are different criteria for what makes a bat illegal in the different levels of baseball, so let’s examine what baseball bat modifications are allowed and which are illegal at the different levels.

What Makes A Baseball Bat Illegal In Baseball?

Closeup of three baseball bats resting vertically on a tan wall and a wooden floor

When we think of an illegal baseball bat, we tend to think of players tampering with their bat to gain an advantage. While this is true, we should keep in mind that baseball bat manufacturers must also adhere to the rules.

Baseball bat manufacturers are also constantly looking to improve their bats so players will prefer their bats over those of another manufacturer. However, there is a fine line that these modifications are walking, some of which could result in the bat being declared illegal at certain levels of the game.

Some bat modifications are illegal across all leagues of the game, while other types of bats are only illegal in certain levels of the game.

We will take a look at what baseball bats and modifications to bats are illegal across the board and then examine which types of bats and modifications are illegal at specific levels of the game.

Baseball Bat Shaving Is Illegal

Bat shaving is a process that is done mostly on composite bats to enhance the performance of the bat. Shaving the bat has the potential to add 30 to 60-feet to the distance of the ball off of the bat.

Bat shaving is an illegal modification where the end cap is removed from the bat, layers of material are removed from the inside of the bat, and the end cap is replaced. Bat shaving increases the “springiness” of the bat for a short time, but it also reduces the lifespan of the bat.

Bat shaving not only makes the bat springier but also removes weight from the bat by the use of a lathe, which makes it easier for the batter to swing the bat. The combination of the additional springiness and the faster swing allows the ball to be hit further distances.

The thinning out of the inner layers of the bat makes the bat springier, which will launch the ball further. The process also weakens the structural integrity of the bat, which could result in the bat shattering on impact with the ball.

Bat shaving services are often blatantly offered, which promotes the misconception that this practice is acceptable, but bat shaving is generally illegal in all types of baseball leagues.

To see an example of how a bat is shaved, check out the YouTube clip below.

Baseball Bat Corking Is Not Permitted

Baseball bat corking is a process performed on wood bats to increase the bat’s performance by improving the trampoline effect of the bat and making the bat lighter to swing.

The corking of a baseball bat is an illegal modification of a wooden baseball bat that involves drilling a 1-inch hole vertically from the end of the bat about 6-inches deep down the center of the barrel of the baseball bat. The cavity is filled with cork or rubber balls and the hole at the end of the bat is re-sealed.

The hole at the end of the bat is filled in an attempt to disguise the modification to the bat and avoid detection. The practice of corking weakens the bat, and the bat is often discovered as having been corked when it breaks during an at-bat.

Contrary to most people’s beliefs, scientific tests have actually proven the corking of a wooden bat offers no performance enhancement to the bat at all!

Although bat corking is primarily done with wooden bats, corking is sometimes done on aluminum bats. The end cap of the aluminum bat is removed, the barrel of the bat is filled with tennis balls, and the end cap is replaced. Bat corking is also deemed illegal for all types of baseball leagues.

For a visual reference on bat corking, below is a great demonstration of how someone might go about corking a bat.

Baseball Bat Painting Is Illegal

Baseball bat painting is a generic term used for changing the appearance of an illegal bat to make it appear legal. Painting a bat includes not only covering identifying markers on the bat but also sanding these identifying markings off the bat in an attempt to hide the use of a bat that is not legal in the game.

To paint a baseball bat, players will take an illegal bat and alter its appearance by sanding the bat, removing logos, adding logos, and painting the bat so that its appearance matches a bat that umpires believe to be legal. 

Painting a bat, removing decals, adding fake decals or markings to a baseball bat to disguise an illegal bat is against the rules of baseball. Use of a bat that is altered to hide an illegal bat is not allowed in any baseball league.

Using Bats With Illegal Drop Weights

The drop weight of a baseball bat is a number that compares the length and weight of a baseball bat. The drop weight is also sometimes referred to as the “bat drop”.

The drop weight is a negative number that is achieved by subtracting the weight of the baseball bat in ounces from the length of the bat in inches.

There are regulations within each league relating to the minimum and maximum drop weights or drop that a bat can be rated at. Using a bat that has a drop weight outside of these regulations is illegal and can result in penalty action taken against the player by the game officials.

For example, once players reach the Senior League of Little League (age 13 and above), the drop weight is -3. This means that if a bat is 31 inches long, the weight can not be less than 28 ounces.

Since the regulations for the drop of the bat will vary from league to league, it is best to consult with your league for the correct range before buying a bat.

Baseball Bat Weighting Is Illegal

Adjusting the weight of a baseball bat will affect the performance of the bat. Increasing the weight will increase the force with which the ball can be struck, and decreasing the weight will make the bat faster to swing. 

Bat weighting is adjusting the weight of the bat to increase or decrease the factory weight of the bat. The weight is normally adjusted at the bat’s end cap, and the endcap is replaced to hide the illegal adjustment. Changing the performance and drop weight of the bat is illegal

The practice of weighting the bat is sometimes referred to as “end loading” because this is the location of the bat where the loading or weighting of the bat is normally done.

Flat Surface Baseball Bats Are Illegal

In the early days of baseball, some bats were constructed with a flat surface, usually on the top of the bat. This flat surface was traditionally used when bunting the ball.

Flat-surfaced bats or bats with bunting surfaces are not legal bats in the game of baseball. Bats with flat surfaces are usually wooden bats with the top surface smoothed to provide a flat surface for bunting the ball.

Grooved Baseball Bats Are Illegal

Grooves in a baseball bat can affect the flight of the ball after the ball has been struck by the bat. Grooves on a baseball bat will impact the spin of the ball, which can alter the way the ball behaves in the air after the strike.

Grooves in a baseball bat are illegal because the inconsistent surface of the bat will change the way a ball reacts after being hit. Grooves will make the ball follow a less predictable flight path and pose a hazard to fielders attempting to catch the ball.

Illegal Substances On A Baseball Bat

Coating the baseball bat with certain substances can result in the bat being declared illegal for gameplay which means you need to be aware of these rules to avoid infringement.

Coating a baseball bat with wax, paraffin, pine tar, or any other substance that affects the flight or rotation of the ball makes the bat illegal, and the bat will be removed from the game. Substances can be used on the handle, but usually no higher than 18-inches from the base of the handle.

Players are allowed to use substances on the handle of the bat to improve their grip. The substance that is most often used for this purpose is pine tar. Whatever substance or material is used to improve grip, it must not extend part 18-inches up the handle of the bat.

If substances are used on the barrel of the bat, it will affect the reaction of the ball and give the batter an unfair advantage.

Major League Legal Bats

In Major league baseball, the speed and power with which the ball is hit can launch the ball at dangerous speeds, which has resulted in some limitations being imposed for bats in this professional league.

Only wood bats are allowed in the MLB, which slows down the speed of the ball and limits ball travel. These limitations are implemented for safety reasons for players in the outfield as well as for spectators in the crowds.

White bats are also not allowed in the major league because a white ball is not visible against a white bat which can be a safety issue for a pitcher if the ball is struck directly back towards the pitcher. The pitcher could have a delayed visual of the ball against the white bat, preventing him from taking evasive action.

Bats must not be more than 2.61-inches in diameter and cannot be more than 42-inches in length from the bottom of the handle to the end cap of the bat.

Minor League Baseball Legal Bats

Minor league baseball teams are the training grounds for major league players and where Major League teams can look at potential prospects to bring up.

Because the minor league players are expected to play baseball at the same intensity as the major league players, the batting regulations for this league are the same as the major league’s regulations.

College Baseball Legal Bats

In college-level baseball, the bats that are used are the same dimensions as those used in major and minor league baseball, but the bat can be of wood, aluminum, or composite material construction.

Other than the composition of the bat and the necessity of the bat being BBCOR rated, the specifications of the bats used for college baseball are the same as for the minor and major leagues.

High School Baseball Legal Bats

Baseball at high school level has different rules to major and minor league baseball when it comes to bat regulations.

Players are allowed to use aluminum, composite or wooden bats at this level. A composite alloy or an aluminum bat is often the bat of choice at this level because of the greater distance that these bats can hit. 

Players are interested in increasing their batting averages to attract the attention of recruiters for college and the further hitting aluminum bats allow them to improve their batting average.

Baseball bats at high school level cannot be more than 2 ⅝ inches in diameter and generally no longer than 34-inches. The bats also need to be BBCOR rated bats, and with a drop of no more than -3.

Little League Baseball Bat Rules

Little League baseball players are generally between the ages of 4 and 16 years old, which changes the regulations of the size and type of bats that are suitable for these players.

Below is a chart, put together with data from the Bat Rules page of Little League’s website, that outlines the aluminum bat rules for the different levels of Little League. If a bat falls outside of these rules, it can be ruled an illegal bat and be removed from the game.

Each division of Little League must also meet the USABat standards or the Batted Ball Coefficient of Restitution (BBCOR) standards.

DivisionBat LengthBat DropBat Barrel Diameter
Tee Ball26″ and belowN/AN/A
Minor / Major (aluminum bats)33″ and belowN/AMax of 2 ⅝ inches
Intermediate34″ and belowN/AMax of 2 ⅝ inches
Senior36″ and below-3Max of 2 ⅝ inches
Little League Challenger33″ and belowN/AMax of 2 ⅝ inches
Senior League Challenger36″ and below-3Max of 2 ⅝ inches


Each level of baseball has its regulations regarding the size, diameter, and drop of the bat that can be used, and any bat that is outside of these specifications is considered an illegal bat for that league.

However, a bat that has been tampered with and modified to enhance the performance of the bat is illegal across all levels of the game.

As the rules of the game change and specifications for bats change, certain bats that were previously considered legal have lost their certifications and are no longer legal for the game. It is always beneficial to examine the rules for the particular level of baseball that you are playing to make sure you get a legal bat.

Most leagues will have a list of bats that are no longer considered suitable to be used for official games. If you have one of these bats it can still be used as a practice bat, but a legal one will be required for game day!

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Steve Nelson

I'm the owner of Baseball Training World. I live in Denver, Colorado and I enjoy playing baseball in an adult baseball team in the surrounding area. Read more about Steve Nelson.

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