catch somebody off guard
throw somebody off guard
take somebody off guard

Caught off-guard, I dropped the phone and buried my face in my hands.

Caught off-guard, Shamil let his face show naked confusion for a moment.

Beauty had become an abstraction; she was never caught off-guard by it.

Caught off-guard, Tom wasn't sure what to say next.

And to be caught off-guard was most definitely a weakness.

"I think a lot of us were initially caught off-guard by how effective it was," he said.

She seemed to be caught off-guard by my downright chipper tone.

What has caught many off-guard is the support, or lack thereof.

She seemed to be caught off-guard by the question.

I quickly put my head down, as though deeply ashamed, nearly caught off-guard by the abrupt, unexpected beginning of the game I'd decided to play.