This knot is also called shosei musubi and since you can move easily with this knot and it is not likely to get loose, it is also used for martial arts, but it is an informal method of wearing hakama.
書生結びともいい、動きやすく結び目がゆるみにくいので、武道などでもちいられるが、袴のはきかたとしては略式。