When you're citing to cases (most commonly, federal circuit court cases), you have to put the Circuit number in the year parenthetical. Example: (4th Cir. 1986). The problem is that Word likes to raise up the "th" so that it looks like this: 4th, which is incorrect. Word does this automatically so it's up to you to fix it.
How do you fix it? The easiest way is to hit the "undo" button or press Ctrl-Z. It will undo the superscript and you can continue. Another way is to ensure that you don't hit the spacebar after your "4th" - put the spaces in advance. That one takes a bit more forethought.
The final way to fix this is to get Word to stop superscripting automatically. Go to Tools | AutoCorrect Options, and click the AutoFormat As You Type tab. Then, deselect the Ordinals (1st) With Superscript check box and click OK.
Hope this helps!