Without thinking about it twice my answer to the question is YES manager are sole responsible for their team's performance. My reason for saying this is because;

Before i will give my reasons, I will ask a practical life question,which is assuming a company is not performing to expectations or collapse, who is the person to be blamed?

If your answer to the question above is the manager then I do not see the reasons why you will not agree with me. Manager are sole responsible for the success of their company likewise their team. I therefore think managers are sole responsible for their teams performance.

Managers are given everything they need in order for them to perform and who therefore should should we blame. Managers are also given the chance to make changes in the course of play if their players are not performing making them the sole responsible for their teams performance.