Baseball’s mound has evolved over the years.
Back in the late 1800s, it was 45 feet from home plate and the pitcher could take a couple of steps with the ball when throwing. Later, the pitcher had a 6-foot-square box as the designated area and had to stay within that box when throwing. The mound was initially defined in the rules in the early 1900s with the pitching rubber at a height of no more than 15 inches above home plate. Because mounds were at varying heights up to 15 inches, the rule was changed in the 1950s, setting 15 inches as the uniform height. Baseball became a pitcher’s game. In the late 1960s, pitcher Bob Gibson had an ERA of 1.12 and MLB’s top hitter, Carl Yastrzemski, was batting .301. During the 1968 season, over one-fifth of all MLB games were shutouts. The rule was officially changed in 1969, establishing the height of the pitching rubber at 10 inches above home plate—period—not 10 inches above the grass. That rule changed the way the game was played. At 15 inches, pitchers were told to “stand tall and fall.” With the change to 10 inches, it became “drop and drive.” The pitchers would drop down and push off from their right or left leg.
That 10-inch height is mandatory for major and minor league baseball, NCAA Baseball and most high school programs. (Check the official governing body for rules at each level of play.)
This is the method I use for new construction or total reconstruction of a mound. There are many other methods, but I’ve found this is the simplest way.
You’ll need a plate compactor, hand tamp, landscape rake, shovel, level board, hose and a water source. I prefer the professional block-type, four-way pitching rubber. You can flip it each year and get four years of use from it.
The most important thing you need is the clay. I suggest using two types: a harder clay on the plateau and landing area and your regular infield mix for the sides and back of the mound. The harder mix has more clay, with a typical mix about 40 percent sand, 40 to 50 percent clay and 10 to 20 percent silt. The infield mix for the rest of the mound is typically about 60 percent sand, 30 percent clay and 10 percent silt. Suppliers offer several options in bagged mound mixes, some of which come partially moist, some almost muddy and some as dry as desert sand. Be aware of those factors as you evaluate your clay sources. Any of the commercially bagged, vendor-provided mound mixes are heavy in clay and good to work with. When you purchase the material from a vendor, you know you’ll be getting the same thing each time. Bricks are also available for the harder clay. Some people prefer these, which are packaged moist and ready to go into the ground. Others prefer the bagged mixes for more flexibility in establishing moisture levels.
You’ll want to have 8 to 10 tons of clay available to build the mound; 2 tons of the harder clay and 6 to 8 tons of the infield mix. You’ll need wheelbarrows or utility vehicles for loading and unloading it—and people to help move it.
The most accurate way to set your distances and heights is to use a transit with a laser. If you don’t have access to this, you can use a string line run between steel spikes with a bubble level that you clip onto the string. Or, you can build a slope board.
Tackling the task
Plan for the proper orientation when constructing a new field or when building a mound for practice purposes. You’ll want the line from home plate through the pitcher’s mound to second base to run east-northeast so the batter isn’t looking into the sun when facing the pitcher. As you prepare to construct the mound, use the transit and laser or string lines to make sure home plate, the pitcher’s mound and second base are accurately aligned and everything is square.
For a regulation MLB field, the distance from the back of the home plate to the front of the pitching rubber is 60 feet 6 inches. The typical pitcher’s mound is an 18-foot circle with the center of the pitching mound 18 inches in front of the pitching rubber. That makes the measurement from the back of the home plate to the center of the pitcher’s mound 59 feet. Too often, the rubber is accidentally placed in the center of the pitcher’s mound so be sure you have the measurements right.
If you’re using the string line, place one steel spike behind the pitching rubber location and one just beyond home plate. Put a pin at the 59-foot point in the center of the mound area and stretch a 9-foot line out from it, moving it all around the pin to mark the outer line of the 18-foot circle. If the grass is already in place, protect it with geotextile and plywood while you’re building the mound.
Leave the pin in the center and place a second pin where the pitching rubber is going to be and mark the pin at 10 inches above home plate. Then, start bringing in the clay to form the base of the mound. Establishing the right moisture content within the clay mix is the key to building the mound. That consistency has been described as just a bit drier than that of Play-Doh when it first comes out of the can. It’s one of the instances where the science and art of sports field management mesh, learning by doing what that right consistency is given the material being used, the outside temperatures and humidity levels, sun, shade or cloud cover, wind speeds and direction. These factors vary daily—and often hourly—and make a difference in the formula that will keep the mix at just the right moisture level.
That’s why you will build the mound in 1-inch levels, creating the degree of moisture you want in each level so it will be just tacky enough for the new layer to adhere to the previous one. Use a tamp to compact each level. It’s important that the hard clay used to build the plateau and landing area is a minimum of 6 to 8 inches deep. You can put down plastic or wrap the tamp with a towel or piece of landscape fabric to keep it from sticking to the clay. You can’t add soil conditioner between these layers, as that will keep them from bonding together. Check the measurements of the height, using the transit and laser or the string line, with every lift of clay.
When you’ve built up the subbase with hard clay at the 60-foot-6-inch area to a 10-inch height, construct the plateau 5 feet wide by 34 inches deep. Position the front of the pitching rubber 60 feet 6 inches from the back of home plate. Set it firmly in place, making sure it is level across the length and width, with the top surface exactly 10 inches above the level of home plate. Draw a centerline through the pitching rubber and run a string from home plate to second base to confirm the rubber is centered.
With the pitching rubber in place and the plateau completed, you can begin to build the slope toward the front of the mound. Begin the slope 6 inches in front of the toe plate creating a fall of 1 inch per each foot. Double-check the accuracy of the slope using the transit and laser or the string line.
You’ll be using the harder mound clay to create the pie-shaped front slope of the mound, as this section will provide the landing area for the pitcher. Use the same method of clay mix, water and tamping, working in 1-inch increments.
You’ll use the infield mix to construct the remainder of the mound. Begin working from the back edge of the plateau using the same layering process. Use the edge of the slope board or a large wooden plank, positioning the top edge on the back of the plateau area and the other edge of the board on the edge of the grass to guide the degree of slope for the back and sides of the mound. Looking at the mound from the front as a clock face, you’ll be completing roughly the area from 9 a.m. to 3 p.m. to transition into the wedge in the front of the mound. You’ll want a smooth area of slope for the back and sides so that the side section precisely meets the edge of the pie-shaped wedge that is the front of the mound. Upon completion, the mound should look like a continuous circle with no indication that different materials have been used.
The dimensions, working from the outer edges of the 5-foot-by-34-inch plateau, are mathematically accurate to make the back and side segments a perfect fit. They tie into the wedge with the 1-inch to 1-foot fall of the front slope that begins 6 inches in front of the pitching rubber.
Once the mound is completed, top it with a 1/8-inch layer of infield conditioner so it won’t stick to the tamp. Then, cover the mound with a tarp and keep it covered to prevent it from drying out and cracking. Once the mound is properly constructed, you’ll have only the easier, but ongoing, task of managing the moisture level as you repair the mound after every practice and game.
Murray Cook is president of the BrightView Sports Turf Division and past president of the Sports Turf Managers Association.