Do you have to overruff?

It depends on the convention: in the strictest version, yes, you must overruff (play a higher trump) when you ruff after an opponent.

What "overruffing" means

To overruff is to play a higher trump than the one already on the table. The question arises when you can't follow the led suit, an opponent has already ruffed, and you hold trumps.

The strict rule

In the most common version of the rules, you must overruff if you can, that is, play a trump higher than the opponent's. If you only hold weaker trumps, you must still play one (you "undertrump" by obligation) for lack of a better option.

Convention: overruff only over opponents

The duty to overruff applies only when an opponent leads the trick. If your partner ruffed and is master, you don't have to overruff them. Some tables relax the rule and don't require overruffing at all: agree before the game to avoid disputes.

See also

FAQ

Must you overruff in coinche?

In the strict version of the rules, yes: if an opponent has ruffed and you can play a higher trump, you must. Some tables don't enforce this.

Do you have to overruff your partner's trick?

No. The duty to overruff only applies to tricks led by an opponent. If your partner is master, you don't overruff them.