Some people who have lost their hair due to chemotherapy use baseball caps with ponytails attached to them in place of wigs. Baseball hats with ponytails can also be suitable for costuming or as a joke.
Several companies sell baseball caps with wigs attached so cancer survivors can simulate a casual style. Some caps feature loose strands that survivors can pull back into a braid or ponytail, while others are already styled in a ponytail.
Some companies sell caps with ponytails that aren't meant to simulate real hair. People with short hair sometimes put them on as a joke. However, it's also possible to wear such caps as part of a costume.