spring upon (?.)
- ambush
- astonish
- bushwhack
- catch at
- catch off-guard
- catch unawares
- come from behind
- come upon unexpectedly
- do the unexpected
- drop in on
- fasten upon
- jump
- jump at
- pounce upon
- pull up short
- scramble for
- seize on
- snap at
- snatch at
- spring a surprise
- surprise
- swoop down upon
- take by surprise
- take short
- take unawares