I have been a vegetarian for over ten years. Mainly due to environmental/ecological concerns that for any animal-based concern.
A vegetarian diet can give you just about all of the essential vitamins, fuel sources, protein, minerals, etc., needed for sports, as will a meat-based diet. I believe there is a B-complex that's only available in 1-2 vegetables, but I take supplements to get it. Also, I have to use some supplements to get things like Omega-3s which come more naturally in meat.
It will be harder for someone who is a vegan, but if one is a lacto-ovo (eggs and diary), they won't notice much difference nutritionally if they put a little effort into their diet. If you still enjoy the "taste" of meat, some of the new soy-based mtea alternatives such as chicken fingers, fake ribs, etc., are pretty tasty, if high in fat and salt.
Not trying to convert anyone...just giving my .02.