How do fighters watch the other fighter?

allan green watches his own feet

they close their eyes

When I spar, my vision is usually right down the center. Occasionally I'll watch one hand or the other if I'm trying to set a trap. Every once and a while I'll look at their eyes to try and gauge where they are mentally in the round to plan my next move. But most of the of the round, I'm looking in the middle so I can see all their movements indirectly without missing anything.