Python game

from tkinter import *
from random import randrange

### DEFS

# directions
def move_ball_right_down():
    global x, y, dx, dy

    x, y = x + dx, y + dy

    can.coords(ball, x-r, y-r, x+r, y+r)

def move_ball_left_up():
    global x, y, dx, dy

    x, y = x - dx, y - dy

    can.coords(ball, x-r, y-r, x+r, y+r)


def move_ball():
    global flag, x, y, moving

    if moving == True:
        move_ball_right_down()
    if moving == False:
        move_ball_left_up()

    if x <= 20 or y <= 20:
        moving = True
    if x >= 480 or y >= 480:
        moving = False


    if flag > 0:
        win.after(50, move_ball)


def click_ball(event):
    global x, y, points, ball, r, dx, flag

    if flag == 1 and\
       event.x <= x + r and event.x >= x - r and\
       event.y <= y + r and event.y >= y - r:

        points = points + 1
        lab2.configure(text = "Points: " + str(points))

        r = r - 1
        dx = dx + 1


        can.coords(ball, x-r, y-r, x+r, y+r)

        pal = ["red", "green", "white", "blue", "black", "yellow", "magenta"]
        m = randrange(7)
        color = pal[m]

        can.itemconfig(ball, fill = color)

    if points == 15:
        lab2.configure(text = "Points: " + str(points) + " - You won!", fg = "green")
        flag = 0


def start():    # start the game
    global flag
    if flag == 0 and points < 15:
        flag = 1
        move_ball()

def pause():    # pause the game
    global flag
    flag = 0

def restart():
    global points, r, x, y, flag, dx

    x, y = 250, 250
    r = 20
    points = 0
    dx, dy = 10, 10
    moving = True

    can.coords(ball, x-r, y-r, x+r, y+r)
    can.itemconfig(ball, fill = "red")
    lab2.configure(text = "Points: " + str(points))

    if flag == 0:
        flag = 1
        move_ball()


### VARS
x, y = 250, 250
dx, dy = 10, 10
r = 20

flag = 0
moving = True

points = 0

### GUI
    # create a WINDOW
win = Tk()
win.title("Clicky game")

    # create a CANVAS
can = Canvas(win, height = 500, width = 500, bg = "light grey")
can.grid(row = 3, column = 1, columnspan = 3, sticky = N)
can.bind("<Button-1>", click_ball)

    # create LABELS
lab  = Label(win, text = "Click on the 'Start' button, than catch the ball!")
lab.grid(row = 1, column = 2, sticky = N, pady = 2)

lab2 = Label(win, text = "Points: 0", fg = "red")
lab2.grid(row = 2, column = 2, sticky = N, pady = 2)

    # add a BALL
ball = can.create_oval(x-r, y-r, x+r, y+r, fill = "red")

    # create BUTTONS
but1 = Button(win, text = "Quit", command = win.destroy)
but1.grid(row = 4, column = 3, sticky = E, padx = 5, pady = 5)

but2 = Button(win, text = "Start", command = start)
but2.grid(row = 4, column = 1, sticky = W, padx = 10, pady = 5)

but3 = Button(win, text = "Pause", command = pause)
but3.grid(row = 4, column = 1, sticky = E, padx = 10, pady = 5)

but4 = Button(win, text = "Restart", command = restart)
but4.grid(row = 4, column = 2, sticky = W, padx = 10, pady = 5)

win.mainloop()