Despite knowledge of the Christian implications of Easter, the Czechs have many traditions around that time.
Typically, this butt whooping is done by male relatives, who use handmade willow sticks with ribbons at the end. It is not supposed to hurt the woman.
Why do the people of the Czech Republic do this? The willow tree is believed to be one of the trees that wakes first after spring, hence it is believed to enhance the fertility and vitality of women.
Some people especially foreigners believe this is barbaric and perpetuating patriarchy and misogyny, but the indigenes have fun with it.