(have) a trick up (one's) sleeve

Translations
иметь козыри в рукаве
The coach always seems to have a trick up his sleeve during tight games.
Тренер всегда, кажется, имеет козыри в рукаве в напряжённых играх.
Definitions
To have a secret plan, idea, or advantage that can be used if needed, often to gain an advantage or solve a problem unexpectedly.