This one should probably be simple for LetsRun.com nation. What the heck was this thing on Yuta Shitara's arm the final 2k of the Tokyo marathon?
Shitara won over a million dollars for running 2:06:11 (he had to go under 2:06:16 to get the big payday) but at the final water stop in addition to getting a drink he whipped the thing out in the photo above that must have been attached to his bottle and put it on his arm. He then kept motoring to the finish and his epic payday.
Full details here with more photos.