Q: Why do sportscasters pronounce “defense” with an emphasis on the “de,” whereas political commentators emphasize the “fense”? Which pronunciation is correct?
A: The usual pronunciation of “defense” is duh-FENSE, except in sports terminology, where it’s generally pronounced DEE-fense.
Similarly, the usual pronunciation of “offense” is uh-FENSE, except in sports terminology, where it’s generally pronounced OFF-ense.
The sportscasters are not incorrect. The variant pronunciations of these words in sports terminology are standard, according to both Merriam-Webster’s Collegiate Dictionary (11th ed.) and The American Heritage Dictionary of the English Language (4th ed.).
I can only speculate as to why sportscasters and athletes pronounce these words as they do.
Perhaps emphasizing the first syllables (OFF and DEE) helps differentiate the two words in a context where both are often being discussed. In close proximity, the normal pronunciations (uh-FENSE, duh-FENSE) might make the difference harder to hear.
Sorry I can’t be more definitive. Maybe a phonologist out there can pitch in.