It doesn’t matter that you are 18 - as long as you still live in your parents house, it’s their rules. No if’s, ands, or buts about it. 
Now, you Mom saying she would break your racket to show you real anger is not right. I can see where you get your anger from. You two sound like you feed off each other.
I think a nice, long, heart to heart with her is in order. Sit down, when you are calm, perhaps this weekend, and try to explain to her that you feel very strongly about the sports you play, and that while you’d love for her to be your champion, you also need her to understand your emotional investment in the sport. And that means sometimes you’ll be angry.
Now, we have only heard one side of this. MtnJim may be right - if you were throwing a tantrum and being a brat, then you deserved it. However, lots and lots of people feel very passionately about the sports or activities they participate in - it’s one of their emotional releases. My date tonight was all sorts of pissed off that the Red Sox lost. BUT, he knows how and when to show that anger. During the game - yes he was pissed. After the game, it was left in the stadium.
Granted, he wasn’t a player. I bet some of those Sox players (that dropped the ball) are still beating up the water coolers.
The bottom line is, coming on here isn’t going to solve the issue - talking with her is.
I have a horrific relationship with my mother as well. I repaired my relationship with my father, and now he is my best friend. Family is very important, something that so many teens fail to realize. You will never, ever have people love you for who you are, unconditionally, like a good family will.
Thats especially important during your teen years! 
I love my two teen boys to bits, but I do want to strangle them sometimes. Or put arsenic in their dinners. Or beat them to death with their mathbooks. But in the end, we do have those kinds of talks, and we are able to understand each other. One of my boys would come “help” me cook dinner every day. He would talk talk talk about his day and everything in his world, totally in my way in the kitchen, and then rush to set the table (wrong) at the last minute. Or would “help” do the dishes - and get water and soap all over the place. I would find food covered dishes in the cupboard a few days later.
I wouldn’t trade those days for anything. 