Teresa really liked and admired her sister Valerie. Valerie was a very good volleyball player, and Teresa felt that she herself was not very good at volleyball. However, when Teresa played volleyball, she started to act and talk like Valerie. Which defense mechanism did Teresa use when she played volleyball?

- Identification.

Explanation:

As per the given description, Teresa employed the Identification defense mechanism as Teresa embraced the behavior of Valerie who is a quality football player. This mechanism was initially proposed by Sandor Ferenczi which is further developed by Anna Freud. Such a mechanism involves a psychological strategy in which the victim acquires the behavioral pattern of the sturdy one in order to prevent damage. Since Teresa is attempting to avoid abuse by adopting Valerie's behavior (acting and talking like her). Thus, it would be characterized as 'identification' defense mechanism.