Juror Eleven makes a suggestion that one of the others does not understand "reasonable doubt". To whom is he directing his remark, and why is the other juror angry?

From the text:

ELEVEN. I beg your pardon. Maybe you don’t understand the term “reasonable doubt.”

SEVEN (angry). What do you mean I don’t understand it? Who do you think you are to talk to me like that? (To all) How do you like this guy? He comes over here running for his life, and before he can even take a big breath he’s telling us how to run the show. The arrogance of him!

Juror Seven is angry because he believes that Juror Eleven is being condescending.... insinuating he believes him to be stupid.