My lens: Tamron 70-200mm 1:2.8

My sons games are daytime. They usually start between 8:00a.m. & noon.
What setting should I use? Thanks.

For action sports, shoot in Shutter Priority mode. You want to freeze action, so 1/500 is going to be a minimum. If you have ample lighting, there should be no problem with 1/1000 or above, which is optimal for football in my opinion.

Would this also apply for slower glass (3.5 / 5.6) using auto ISO?

Well, that's a different story. We're talking about the exposure triangle here (ISO/Shutter/Aperture), and it's always a juggling act. You have to look at it this way: You have two main objectives when shooting sports, stopping action and tack sharp photos.

For stopping action, you need to be above 1/500, period. Football isn't exactly fast-action like racing, but even at 1/500 you're going to see motion blur sometimes. If you can venture up into the 1/640 or 1/800 range and still have decent depth, then that's great. Most professional level (talking about the photographer here, not the players) football photos focus on the player and up to about a 5ft radius around them. That way you also capture a player tackling them or whatever and they are also in sharp focus. No one cares about the guy 10 yards down the field.

So, and this is just me...what I shoot...I try to keep my shutter speed as high as I can and still maintain ISO 200 (in daylight) with as high an aperture as I can. Shutter speed takes first priority, followed by aperture, then ISO. Digital cameras these days don't produce much noise, so ISO is less of a concern until higher levels.

I'm taking some football photos tonight, so I'll post them up.

I was planning on shooting some high school football today. Matter of fact, I was checking the board before I walked out the door when I read your post. Game might be canceled because of the heat. 88F right now. Going to give your advice a try. If not... off to shoot some more birds, but they are hiding, too. Thanks for the input.

EXIF:
D300s
Mode: Shutter Priority
Focal length: 200mm
1/1000 @ f/5.0
ISO 200

O.K., Thanks. Can't wait to try these settings tomorrow a.m.

Anthony is right on with the exposure settings. The other problem you will face is focus. To get the high shutter speed you will probably be using a low f/stop, 2.8, 3.5, 5.6. That means relatively shallow depth of field. Keeping focus on a fast moving subject with a shallow depth of field can be tricky. To keep the focus where I want it I use spot focusing and the focus mode set on "C" continuous. With the shutter button pressed half way down you can track the subject with the focus spot for your best shot and the camera will refocus as the subject moves.

Something else I forgot to mention. You should be able to change the size of your focus spot. You don't mention what camera you are using in your post or in your profile, but on the D90 the spot focus has three sizes, 6mm, 8mm and 12mm. The 8mm setting is the default. You can change the spot focus to 12mm, or whatever larger size your camera allows, and that should make it a little easier to keep the "spot" on target.

Forgot to set the focus & I didn't understand how to set or use spot focusing. My son made his first tackle & I missed it. This was probably the best shot I got that day. Comments, suggestions are welcomed.