Girls, Why does she always go for THAT area when we are play fighting?

Anonymous
Me and my sister occasionally play fight since I moved back in with her and my Mom and we get along and it is fun. But frustratingly now that she is a bit older she is way more rough when play fighting and she seems so much more competitive and just wants to hurt me and win. Pretty much straight away when we start messing around she now just clenches her fist up and holds it up like she is going to punch me and looks right at my balls. She tries to punch me over and over and just goes for my nuts! Luckily she is not big or strong so I can grab her hands and push her away but she has gotten me really bad before by surprise that had me almost in tears.

I'm not sure who taught her to do this and why she thinks it's funny and ok to do but our mom just ignores it.
So my question is really How do I get her to stop? Is this something you did to your brother/father? Why did you do it and what was your reason for aiming there? What made you stop doing it?
Updates
1 y
Thank you all for the answers, just an update. I told my mom and she said she was the one that taught her? She said she taught her to hit boys there to defend herself but she meant in a real situation and she clearly just took that as defending herself even when just playing around.

She is going to talk to her about it to explain what she meant properly. Thanks for the advice!
Girls, Why does she always go for THAT area when we are play fighting?
7 Opinion