According to Sponichi, Katsuya Nomura wasn't sure which player to start: Naoto Watanabe or Kensuke Uchimura.
So what does he do?
He has Watanabe and Uchimura Rock-Scissor-Paper their way into the line-up.
In a short series, you don't know what's going to happen anyway, so why not leave the decision up to chance as well.
This method of picking starters apparently isn't new. Back on September 12, 2004, Hiromitsu Ochiai picked his starter based on the same game of rock-scissor-paper and the winner of the game, DaisukeYamai, ended up tossing a complete game shut-out victory.
The Japanese (myself included I suppose) sure do love a good game of rock-scissor-paper...