할당 오류 이전에 참조 된 지역 변수

저는 코딩을 처음 접했고 제 자신의 게임을 만들려고 노력하고 있습니다. 오류의 의미를 이해하지는 않지만 여기에 내 코드가 있습니다.

import pgzrun
import math
import random

WIDTH = 800                       #5
HEIGHT = 600
CENTER_X = WIDTH/2
CENTER_Y = HEIGHT/2
CENTER = (CENTER_X, CENTER_Y)
FONT_COLOR = (221, 160, 221)      #10
ozol = 0

game_over = False

ozolith = Actor("ozolith")        #15

def draw():
    screen.clear()
    ozolith.draw()
    draw_counters(ozol)           #20

def place_ozolith():
    ozolith.x = CENTER_X
    ozolith.y = CENTER_Y
                                  #25
def draw_counters(ozol):
    screen.draw.text(str(ozol), fontsize=40, center=CENTER, color=FONT_COLOR)

def on_mouse_down(pos):
    if ozolith.collidepoint(pos): #30
        ozol += 1
        place_ozolith
    else:
        quit()
                                  #35
place_ozolith

pgzrun.go()

다음은 오류 메시지입니다.

Traceback (most recent call last):
  File "C:\Program Files\Python38\python-games\GameCraft\GameCraft.py", line 38, in <module>
    pgzrun.go()
  File "C:\Program Files\Python38\lib\site-packages\pgzrun.py", line 31, in go
    run_mod(mod)
  File "C:\Program Files\Python38\lib\site-packages\pgzero\runner.py", line 113, in run_mod
    PGZeroGame(mod).run()
  File "C:\Program Files\Python38\lib\site-packages\pgzero\game.py", line 217, in run
    self.mainloop()
  File "C:\Program Files\Python38\lib\site-packages\pgzero\game.py", line 247, in mainloop
    self.dispatch_event(event)
  File "C:\Program Files\Python38\lib\site-packages\pgzero\game.py", line 172, in dispatch_event
    handler(event)
  File "C:\Program Files\Python38\lib\site-packages\pgzero\game.py", line 164, in new_handler
    return handler(**prepped)
  File "C:\Program Files\Python38\python-games\GameCraft\GameCraft.py", line 31, in on_mouse_down
    ozol += 1
UnboundLocalError: local variable 'ozol' referenced before assignment

왼쪽 상단에 붙어있는 이미지를 클릭하면 발생합니다.