According to Hairfinder, a shag haircut can be long, medium or short. A shag haircut involves layering the hair so that it becomes increasingly long as it progresses from the top of the head to the neckline.
Section the hair and cut bangs
To begin cutting a shag haircut, section the hair in layers and leave down a perimeter around the head and for the bangs. Cut the bangs to the desired length, then move along the hairline to the back, creating a guide for the shape and length of the haircut.
Cut the top section
After creating a guide, take down the top section of hair and comb a small part from the middle up towards the top of the head. This piece of hair becomes the guide for length for the rest of the top section. Then, take thin vertical pieces of hair, comb them straight up and cut to the desired length, using the middle piece as a guide so that the hair is cut in a straight line.
Cut the remaining sections and clean up the haircut
After cutting the top section, lower the remaining sections of hair and do the same procedure, using a middle piece as a length guide. Blend the bottommost and longest sections of hair with the perimeter guide cut in Step 1 to maintain the desired shape. When all the hair is cut, comb it outward horizontally and look for hair that may have been missed. Check the evenness of the cut and make changes as necessary. After the shag is cut, it can be styled as desired.