pygame.error: video system not initialized

if event.type == pygame.quit():

In the line above, you're calling pygame.quit() which is a function, while what you really want is the constant pygame.QUIT. By calling pygame.quit(), pygame is no longer initialized, which is why you get that error.

Thus, changing the line to:

if event.type == pygame.QUIT: # Note the capitalization

Will solve your problem.

It's important to note that pygame.quit() will not exit the program.