Short version:
Ok, ran some quick numbers. Median for Mendenhall was 3 ypc and population mean confidence interval for 98% (fancy stats way of saying that if he had an infinite number of rushes against USC's defense, in what range would we expect to find the mean ypc 98% of the time) is (-2.19,20.4) ypc. That's ridiculously big, and it's a direct result of the standard deviation being so big (20.01 yards).
The median is a nicer number than the mean because it tells us precisely where the 50% cutoff is. In Mendenhall's game against USC, it tells us that 50% of his runs were for more than 3 yards.
Long version (or "Math is Messy"):
Unfortunately this really doesn't help the issue; the problem is that, statistically speaking, n=17 is a small sample size. I really shouldn't even assume that the stats are roughly normal for this small a sample, and should use a t-test, but I'm lazy and don't know the standard variable values for t-tests off the top of my head.
Just for a basis of comparison, Beanie's game against scUM had a median of 4 ypc, standard deviation of 10.6 yards, and a population mean confidence interval for 98% of (1.7,9.6) ypc. Again, a series of long runs (62, 24, 16, 12, 12) ensure that. The stats are a little better in this case, too, because the number of samples (n=39) is above the rule of thumb cutoff of n=30.
I may go ahead and try to do some more stats for the entire season, as long as I'm at this, but I'm not thrilled about transcribing hundreds of data points. I guess it could be worse though.