In basketball, playing good defense is all about working with your teammates to prevent the other team from scoring.
In order to do that, you have to be able to see all five players on the other team at all times. This is why you hear many coaches say, “Keep your head on a swivel” in different sports.
Really, they just mean keep your head and eyes moving so you can see everything around you.
Because when you lose track of someone – even when it’s not necessarily the player you are guarding at the time – something like this can happen.