What does "black eyes" mean in this situation?
I've learnt an English text which included these sentences:
Why do people play football? It's a stupid game, and dangerous too. Twenty-two men fight for two hours to kick a ball into a net. They get more black eyes than goals.
I just didn't know why the person said "They get more black eyes than goals.". Can you tell me what does "black eyes" mean in this situation?
Thanks in advance.