catch someone cold
catch (one) cold
1. To surprise someone with something. In this usage, a noun or pronoun is always used between "catch" and "cold." News that I'd gotten the promotion really caught me cold—I didn't think they were seriously considering me for it!
2. To surprise an opponent in order to gain an advantage. If we can catch their defense cold, we should be able to tie the game.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
catch someone coldmainly BRITISH, JOURNALISM
In sport, if you catch someone cold, you defeat them or gain points by attacking when they are not prepared. Northern, seeking their eighth successive League win, were caught cold by Castleford. Dewsbury managed a 29-14 win after Barrow had caught them cold to lead 8-4 at the interval.
Collins COBUILD Idioms Dictionary, 3rd ed. © HarperCollins Publishers 2012