large jpeg on Canon set for landscape gives a degree of in camera sharpening and saves time in postwork.
Be very very careful regards legal aspect of your project, school sports ground is private land and you will need permission for each person that you photograph, it is a legal minefield and many pros have decided to stopcovering these events.
Yes I can hear you saying that it is not logical because many parents take snaps of the event, but as soon as you start making money you have to take a pro view and cover the legal side.

I know. We all have our CIB checks etc. even though I am already cleared for the Cubs / Scouts it needs doing for every type of event.
We are the official Photographic team so we have vests and passes etc. and 2 of the lads are fully qualified NHS 1st aiders…altough obviously cant mend broken things or give medicines.

As for shooting in Raw at such events, well there will be no time to post process the images on the day. The PC’s being used do not have lightroom or Canon DPP or Photoshop CS 5.
And, I will need to use lots of continious shooting, Raw takes too long to write to the card/doesn’t write enough from the cache memory etc.
I can make a hell of a difference to a poor Jpeg in Genuine Fractals! ;-).
I’ve upped a 2mp picture from a cheap Kodak point and shoot, (Which was cropped more than 50%) good enough to print A3 with no discernable tiling or edge teeth. It was a portrait too, so I had to get the eyes etc. looking great.

Short experiments today, just using MS Picture Manager for viewing….
Camera set to best qual Jpeg.
User Def 1, Picture style Standard.
Sharpness at 7
Contrast and Saturation at 1 (Might give the sat at 2 on the day if it’s dull and I might set the contrast at 2 and sacrifice some of the sharpness, acutance is acutance LoL)
Colour tone at null.
Results were perfectly acceptable for the needs.
It took about 11 shots before there was a pause in the writing to card. That of course is variable to the amount of data in the picture.