Fig.: to remain alert and attentive; stay focused on the matter at hand

I'm not telling you to drive slowly, because I know you won't, but keep your eye on the ball!

Non ti dico di guidare piano perché so che non lo farai, ma stai all'occhio!

Time was tight, the job was difficult. Luckily, I was able to keep my eye on the ball until the end and did a great job on time

Il tempo era poco, il lavoro difficile. Fortunatamente sono riuscito a stare concentrato fino alla fine e ho completato un gran bel lavoro nei tempi previsti

This expression alludes to numerous sports in which players must watch a ball's path (Ammer)