Closer question

It has been a while since my last game, the beginning of May to be exact, and it seems like there have been some changes. I was wondering what changes to the game have occurred since then? In particular what does the new "C" rating mean that I see a couple of current closers with (Papelbon/Nathan for example)?

C (Closer) is only for 20xx games. Not in use here.

Thank you.