Answer: Discharge by impossibility of performance
Explanation:
Discharge by impossibility of performance is defined as the already known impossibility of execution of performance or task. In this type of case, parties involved in the contract or agreement have knowledge about performance promise is impossible to accomplish. It does not matter even if they are involved in agreement.
According to the situation described in question, discharge of Richmond is based on discharge by impossibility of performance . Even if Richmond is involved in contract with soccer team , it is impossible for him to perform further as he has injured his right leg in accident.Thus, impossibility of performance is already known by both the parties.