Juror #6 is probably the most invisible juror of the entire bunch. He only has a handful of lines in the movie, and he tends to come across as a guy who's willing to change his mind if people can convince him. As he says toward the beginning of the movie, "I don't know. I started to be convinced, you know, with the testimony from those people across the hall. Didn't they say something about an argument between the father and the boy around seven o'clock that night? I mean, I can be wrong."
This kind of talk shows us that he has a fair mind and simply thinks the kid is guilty, although he's willing to admit he could be wrong.
The only time Juror #6 shows a strong personality is when he scolds Juror #3 for speaking rudely to the elderly Juror #9. He hasn't taken a strong stand on the case yet, but he's more than happy to put his cards on the table when he says, "You oughta have more respect, mister. You say stuff like that to him [#9] again... I'm gonna lay you out." So that's what we've got from this guy—maybe he's not all that smart, but he's open-minded and quick to defend someone who's getting bullied.