摔了一跤的英文说法是 "take a spill" 或 "fall down". 这个短语来源于英语中 "spill" 这个动词，指的是 "摔倒，滑倒" 等意思。例如：

I took a spill on the ice and skinned my knee.

He took a spill off his bike and scraped his elbow.

若要表示 "摔了一跤" 这个概念，可以使用 "take a spill" 或 "fall down" 这两个短语来表示。例如：

I took a spill while I was running and bruised my hip.

She took a spill down the stairs and sprained her ankle.