Why do guys like to play fight with their gals?

We are both in our 30's but the guy I am dating ( aka boyfriend) is totally into the play fighting. He has dowsed me with water, tackled me to the ground, he bites me hard, always pinches me to the point of screams. And he freaking enjoys it all and then tries to get lovey afterwards. What it is with the play fighting that guys enjoy so much. A tom boy in disguise I enjoy the challenge but no other guy has done this with me.
Why do guys like to play fight with their gals?
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