I agree with brettjr2005. In my opinion, wearing sunglasses is not professional and shows disrespect. You look sloppy, aloof and someone who doesn't seem to want to be there, would rather be at a beach.
Say you went out on the field:
(a) without your striped shirt tucked in, it's flailing about when you're running
(b) had your zipper all the way down on your striped shirt with your thick burly chest hair all out (with the tinted sunglasses too, you're looking like Burt Reynolds)
(c) when you have a long thin blade of hay/grass in your mouth, sticking out, and you're chewing it all game
(d) when your face and hands are all muddy and dirty from doing some sort of work right before the game
(e) wearing your hat on backwards with the rim facing the back
Those are all very similar, to me, to wearing sunglasses.