Glass First, Camera Body Second
Does anyone that has contributed to this thread, actually shoot sports (HS/ U-18), and not from a casual standpoint??? It's a serious question.
I do. And am reporting for duty!
First off, about what I do with what i have. In my senior year of High School I was in the Yearbook class and was the go to photographer in the class for all things sports for the yearbook. At the start of the year I personally had a Canon Rebel XT (350D), a 24-70 2.8L and a 580EX2 flash. Being a photographer for the yearbook, I had access to the sidelines of games, something which few others had and of course the coach will have. Even with the closeness of what I had to the action relative to the stands for football games, the 24-70 lens was completely useless for field action. It was only good for the cheerleaders of the games and some of the fanatical fans my school is known for when I was near the stands.
Because my lens wasn't working out for me at all for what I needed to get for the yearbook, I purchased with my money a Canon 70-200 f/4 L (non is) lens before Homecoming football came around. The only other lens I had thought about getting was the 70-300 Canon lens. I chose the 70-200 lens because of it's focusing speed, constant f/4 aperture, and its build quality.
Once I got that lens I started using the yearbook classes camera as well, putting my 70-200 on the classes Rebel XTi and my 24-70 on my XT.
I now have been helping out with the yearbook in some spare time I have, dropping in occasionally when suggested by the new yearbook teacher, teaching some students some photography tips and helping with other yearbooky admin/design things when I can work around the college and job duties I have. I also have been taking pictures for them because I greatly enjoy it and have become much better at tracking action with all the sports i shoot for, them being: football, XC running, XC skiing, basketball, cheerleading, volleyball, wrestling, and hockey. My primary camera set up for most of those would be my Rebel XT with my 70-200. The only time it ever really struggled with anything was when I did hockey (once!) or with inside sports like basketball or volleyball, which I think calls for the a shorter lens. This lens even works when the sunlight has disappeared completely and the only thing I have in regards to light are the friday night field lights, all the way out til 10 or 10:30pm. Even to you peeps comparing 1D's to 50D's in regards to ISO related picture quality issues and lowlight autofocusing, I still think my experience with what I've detailed proves you can have absolutely wonderful pictures very often with equipment some would call impossible to work with, i.e. old rebel camera bodies.
The 70-200 f/4L lens paired with a used 350D/400D (or 30D/40D, i don't know how much they go for used) will get someone great pictures often if the camera is set up properly and the person taking the pictures has some skill, or some great pictures occasionally if the skill is a bit lacking anyway. I think that would be the ultimate setup for a budget of under a thousand dollars for distant sports pictures.
If a shorter lens is called for, I suppose the previously recommended 28-135 is will do well. I have used my uncles (never for sports though) but from what I remember, it was good, even compared to my L lenses.