For the next few weekends all over Japan, mothers will be up at dawn preparing elaborate bentō, while fathers toting plastic mats will set off to school to claim a prime spot (or perhaps vice versa in some households). It's undōkai season!
Undōkai is sometimes described as a "field day" or even "athletic meet" in English textbooks, but most foreign parents seem to agree that "sports day" is the best translation, although some junior and senior high schools prefer the term taiikusai (sports festival). Surprisingly, perhaps, it was a visiting naval officer from Britain who came up with the idea originally. The very first Japanese undōkai was held at the Imperial Naval College in 1874, led by an English teacher named Frederick William Strange.
If you have multiple children in different schools, October can turn into one long parade of undōkai. There are also more casual community sports days, open to the whole neighborhood.