footed

To startle someone; to come upon someone unawares and/or when he or she is unprepared. Usually used in the past tense. The security guard caught the thieves flat-footed. That essay question in the exam caught me completely flat-footed.

Clumsy, ponderous, or lumbering in gait or tread. The team's star striker deftly navigated the ball past the heavy-footed defenseman.

to catch a person in the act of doing something wrong. (See also caught red-handed.) Tom was stealing the car when the police drove by and caught him red-handed. Mary tried to cash a forged check at the bank, and the teller caught her red-handed.

to discover someone doing something illegal or wrong (often + doing sth) I caught him red-handed trying to break into my car.

Also, catch in the act. Apprehend someone in the course of wrongdoing, as in The boys were trying to steal a car and the police caught them red-handed, or He tried to cheat on the exam, but his teacher walked in and caught him in the act. The first term referred to blood on a murderer's hands and originally signified only that crime. Later it was extended to any offense. The variant ( catch in the act) is a translation of the Latin in flagrante delicto, part of the Roman code and long used in English law.

Caught unprepared, taken by surprise, as in The reporter's question caught the President flat-footed. This usage comes from one or another sport in which a player should be on his or her toes, ready to act. [c. 1900]