打落水狗

1. • lit. to beat a drowning dog (idiom)
2. • fig. to pulverize an (already defeated) enemy
3. • to hit sb when he's down

Character by character

• 打(dǎ)a semantically light, transitive verb that is combined with various grammatical objects to form compound verbs and verb-object phrases with a diverse range of meanings
• 落(luò)fall or drop
• 水(shuǐ)surname Shui
• 狗(gǒu)dog