Cut out the player's team number using a piece of cardboard.
Ensure that the shirt is face down on a hard surface, and tape the numbers on the back of the cotton shirt by outlining each number with masking tape.
Place a piece of cardboard inside the shirt underneath the numbers, and spray paint evenly around the number; allow shirt to dry.
Peel off the masking tape to reveal the player's uniform number.
Flip the shirt over to the front side, and use the paint pen to spell out the team's name.
Locate a meaningful image or the team's mascot on the computer. Check to be sure that the image is not copyrighted or that there are not any restrictions for its use.
Print the image using a color printer onto transfer paper.
Place the printer image face down on the front of the shirt below the team name, but keep the cardboard inside the shirt. Using a warm iron, gently glide the iron over the image, and allow it to cool. Carefully peel off the transfer paper.