Pair with verbs:
翻跟斗 'do a somersault' (deliberate),
摔跟斗 'take a tumble' (accidental),
栽跟斗 'come a cropper' (literal or figurative - fail badly).
栽跟斗 is the idiom you'll hear when someone screws up at work or in a deal.
跟头 (gēntou) is an interchangeable variant.
