転ぶ
ころぶ · korobu · JLPT N3 · verb-godan
to fall down
転 = turn/roll (as in 回転 rotation); korobu: you roll over and go down
The kanji 転 means to turn or roll, as in 回転 (kaiten, rotation). The reading echoes ころころ (korokoro), the Japanese sound word for something rolling along. So korobu is a tumble: your body turns over and you hit the ground.