I'd like to know if this story is true or false; and, if true, the
name of the university and the year of the address.
Grantland Rice, the legendary sports writer, is said to have been
invited to give the commencement address at an Ivy League school. 
When students at the school learned that the address was to be given
by a "common" sports writer, they raised a big stink.
Mr. Rice stood up to speak and did so, giving his entire address in
Latin.
I believe Mr. Rice graduated with honors as a classics major from a
well-known southern university, perhaps Vanderbilt.

Greetings!

Henry Grantland Rice (1880-1954) was the first superstar sportscaster.
 He was indeed a graduate of Vanderbilt University, with a double
major in Greek and Latin.  He also had a Phi Beta Kappa key.  He is
now best remembered for the famous line (from one of his poems):

 "When the One Great Scorer comes to write against your name/He marks
- not that you won or lost - but how you played the game."

He quite often slipped classical and literary references into his
commentary, such as calling the Notre Dame football team "The Four
Horsemen of the Apocalypse".
Unfortunately, your story about his commencement address in Latin is
unverifiable.  There seems no doubt that he would have been capable of
giving a speech in Latin, given his schooling, but I was able to find
absolutely no evidence or even rumors of the story on several
different search engines.

There is more biographical information on Rice at
http://excellent.com.utk.edu/~journal/Rice.html .   There's an amusing
anecdote about his part in forming the bylaws of the Augusta National
at http://www.nytimes.com/books/first/s/sampson-masters.html .

There are several books written about Rice, listed in a bibliography
at http://www.pubdim.net/baseballlibrary/sabr/tbi/R/Rice_Grantland.tbi.stm
.

Search engines used:
www.google.com
www.lycos.com
www.altavista.com
www.metacrawler.com
groups.google.com

Search terms used:
"grantland rice" latin
grantland rice commencement
grantland rice speech latin
grantland rice biography
"henry g rice" commencement
grantland rice graduation
"grantland rice" "ivy league"

Thanks for your question!

Both the original answer (austin_trill-ga) and the additional comment
(mara-ga) were VERY helpful.  I appreciate the efforts of both
respondents and, moreover, the results they produced.
It seems highly likely that their research will hold up under careful
scrutiny although I do have one more avenue to explore before being
completely confident this is the case.
Whatever the end result is, the two respondents have done a very good
job; and I feel as though their work is well worth the fee I am
paying.

More negative evidence. In the Rice biography How You Played the Game,
an account is given of Rice's (second!) appearance on This Is Your
Life. One of the surprise guests was Grant's Latin teacher. Rice is
quoted as saying, "He taught me the rudiments of Latin..." and
reciting a bit of Latin, just as his teacher walked out onto the
stage. Banter ensues, a small amount of which is recounted, but none
of which makes any reference to an entire commencement address given
in Latin. (p. 503)

I haven't read the entire biography; perhaps von-ga would want to do
that.