UnboundLocalError: local variable 'score' referenced before assignment в игре

пишет UnboundLocalError: local variable 'score' referenced before assignment, когда переменная score должна увеличится на 1

score = 0
from tkinter import *
import random
import time



  class Ball:

    def __init__(self, canvas, paddle, color):
        self.canvas = canvas
        self.paddle = paddle
        self.id = canvas.create_oval(10, 10, 25, 25, fill=color)
        self.canvas.move(self.id, 245, 100)
        starts = [-3, -2, -1, 1, 2, 3]
        random.shuffle(starts)
        self.x = starts[0]
        self.y = -3
        self.canvas_height = self.canvas.winfo_height()
        self.canvas_width = self.canvas.winfo_width()
        self.hit_bottom = False

    def hit_paddle(self, pos):
        paddle_pos = self.canvas.coords(self.paddle.id)
        if pos[2] >= paddle_pos[0] and pos[0] <= paddle_pos[2]:
        if pos[3] >= paddle_pos[1] and pos[3] <= paddle_pos[3]:
            score = score + 1 # как я понял, ошибка где-то тут
            return True
    return False

def draw(self):
    self.canvas.move(self.id, self.x, self.y)
    pos = self.canvas.coords(self.id)
    if pos[1] <= 0:
        self.y = 9
    if pos[3] >= self.canvas_height:
        self.hit_bottom = True
    if self.hit_paddle(pos) == True:
        score = score + 1
        self.y = -9
    if pos[0] <= 0:
        self.x = 9
    if pos[2] >= self.canvas_width:
        self.x = -9
    

class Paddle:
    def __init__(self, canvas, color):
        self.canvas = canvas
        self.id = canvas.create_rectangle(0, 0, 100, 10, fill=color)
        self.canvas.move(self.id, 200, 300)
        self.x = 0
        self.canvas_width = self.canvas.winfo_width()
        self.canvas.bind_all('<KeyPress-Left>', self.turn_left)
        self.canvas.bind_all('<KeyPress-Right>', self.turn_right)

    def draw(self):
        self.canvas.move(self.id, self.x, 0)
        pos = self.canvas.coords(self.id)
        if pos[0] <= 0:
            self.x = 0
        elif pos[2] >= self.canvas_width:
            self.x = 0

    def turn_left(self, evt):
        self.x = -6

    def turn_right(self, evt):
        self.x = 6
        
tk = Tk()
tk.title("Game")
tk.resizable(0, 0)
tk.wm_attributes("-topmost", 1)
canvas = Canvas(tk, width=400, height=500, bd=0, highlightthickness=0)
canvas.pack()
tk.update()

paddle = Paddle(canvas, 'blue')
ball = Ball(canvas, paddle, 'red')

while 1:

if ball.hit_bottom == False:
    ball.draw()
    paddle.draw()