Been a couple of times to the Kassam Stadium & been down that area quite a few times on holiday.
Unless it's changed there were no pubs near the ground. There used to be a bar at a bowling alley, wouldn't be my choice though.
Big car park at the ground but gets full early.
Try the Kings Arms at Sandford on Thames right on the river if it's still open, used to be a Chef & Brewers pub.
Alternatively try the George Inn or British Legion at Littlemore.
We will be heading for Abingdon, much more classy & around 20 to 25mins back into Oxford.Have a good day....I know we will.