According to the full schedule on the official London Olympics web site, a category called "Athletics" begins August 3. No such category is listed on the full schedule on the NBC web site, but a category called "Track & field" begins August 3. Why? In different parts of the English-speaking world, different terms are used for the same thing. In the United States, "athletics" usually has a broader meaning than on the London Olympics web site.
How does the DDC handle this? If you browse the Relative Index for "athletics," you will find:
Athletics (Sports) 796
Athletics (Track and field) 796.42
In the record for 796 Athletic and outdoor sports and games is the note: "Use 796 for athletics covering sports as a whole. Use 796.42 for athletics limited to track and field." The same note is given also at 796.42 Track and field.
A children's book by Clive Gifford published in London in the "Olympic sports" series has the title Athletics. The version of the same book published in Mankato, Minnesota, has the title Track and Field. Both versions are correctly classed in 796.42 Track and field.
The comprehensive number for track and field events is 796.42 Track and field, but a see reference at 796.42 ("For field events, see 796.43") shows that field events by themselves are classed in 796.43 Jumping and throwing. An example of a work classed in a subdivision of 796.43 is Winning Jumps and Pole Vault, classed in 796.432 Jumping. A see reference at 796.432 ("For pole vaulting, see 796.434") shows that 796.432 is the comprehensive number for jumping and pole vaulting, but pole vault by itself is classed in 796.434 Pole vaulting (e.g., The Pole Vault). Incidentally, at 796.434 is a see-also reference pointing to the new number for artistic gymnastics: "See also 796.442 for gymnastic vaulting."
Decathlon and heptathlon, which involve both track events and field events, are named in a class-here note at 796.42 Track and field. An example of a work classed in 796.42 is A Basic Guide to Decathlon.
Postscript: Unlike Michael Panzer, I don't loathe athletics / track and field (see his comment in yesterday's blog entry); indeed, one year in elementary school / primary school I managed to squeak onto the second string of the track team and compete in the broad jump. At 796.432 Jumping "long jump (broad jump)" is named in the including note.