*Copy paste from bug report*
After some testing, the save component to shield rush is not working as in the description. While I constantly land Stunning Shield stuns on EE dogs in Lords of Dust, I have little success knocking down the much weaker cultists on EH or even EN, despite my gear and enhancements/ED points resulting in what should be a very similar DC, against the same save stat. PVP testing in the lobster shows a balance save instead of a fort save (backed up by a paladin with over 100 fort constantly failing against what should be a DC 84 OR 94 fort save, disparity referenced below). The effect itself is called Takedown, and MAY POSSIBLY be related to the problem (same name and icon as the lvl 1 druid spell).
Recreate by taking two characters to the PVP pit, one with Shield Rush, and have at it. Also experiment against higher level mobs (at least epic level, as the skill functions perfectly against the training kobolds in the dojo). Use skills with similar DCs against the same save (fort) as a benchmark for the expected success rate, and compare against the actual success rate of Shield Rush.
Also, the text for the save references "class level", where Stunning Shield and the stun component of the capstone (Shield Champion) reference "character level". Unknown if this is using class level (18) or if it is in fact using characater level (28). (shield rush does not display its dc).