If something catches you off guard, it means that you didn’t expect it. You were surprised/you didn’t see it coming.
Examples from the web:
He’s got a lot of tricky moves, so make sure he doesn’t catch you off guard!
The soldiers moved in quickly,hoping to catch the enemy troops off guard.
I think I caught him off guard when I told him I was resigning.[/vc_column_text][/vc_column][/vc_row]