turtles and sex

Question
I saw a couple of videos of turtles having sex.  Each one showed the male turtle head butting the female...violently.  What is the purpose of the head butting?

Answer
The courtship displays of many animals are fairly violent and can often look like combat. Some turtles and tortoises have rather combative courtships, but most are more gentle. Many pond turtles, for example, use a cheek stroking face to face dance.

Why do so many animals use combative courtships? No one is really sure, but there is obviously some element of domination involved. The hormones and parts of the brain used for sex and combat are also closely related.

I am sorry I cannot help more, but I am not an animal behavior expert!