乘隙而入

chéngxì'érrù

to exploit one's opponent's weakness, or to act when one's opponent is off guard

Wiktionary

Entry Composition

1 乘隙 chéngxì
  1. to seize an opportunity
  2. to exploit (a loophole)
2 而 ér
  1. and
  2. as well as
  3. and so
  4. but (not)
  5. yet (not)
  6. (indicates causal relation)
  7. (indicates change of state)
  8. (indicates contrast)
3 入 rù
  1. to enter; to go into
  2. to join; to become a member of
  3. (bound form) to conform to (as in 入時 rùshí)
  4. abbr. for 入聲 rùshēng
  5. (on product packaging, after {number n} + {classifier}) containing (n pieces) (from Japanese 入 "iri")