to attack someone suddenly and unexpectedly

The soldiers fell on the villagers and seized all their weapons. 士兵们袭击了村民，并缴获了所有武器。

If your eyes fall on something, or your sight, eyes, etc. fall on something, you see and notice it.

Her gaze fell upon a small box at the back of the shop. 她的目光落在商店最里面的一个小盒子上。

to start to eat food eagerly

They fell on the bread as if they hadn't eaten for days. 他们扑向面包大吃起来，就好像好多天没吃过东西似的。