Six games were played on Saturday.  No home runs were hit.

Since the start of the two league format, there have only been two other days where six or more games were played and zero home runs were hit: September 13, 1955 (seven games) and May 7, 1958 (six games).

However, Saturday was the first time in NPB history when every team in the league played a game and ended with zero home runs -- double headers were included in the schedule for the previous two occurrences (1955: fourteen teams, six CL and eight PL, one double header, Hiroshima and Yomiuri did not play games; 1958: twelve teams, six teams each, one double header, Toei and Daimai did not play games).

Other interesting stats:

There have only been three days in NPB history where just one home run was hit (does not mention how many games were played): September 13, 1969 (seven games); May 21, 2000 (six games); and August 17, 2007 (six games).

The most home runs hit in one day was thirty-six, set on June 7, 1964 over twelve games.  The most for a six-game day: twenty-eight set on April 7, 1977.

Source: Sponichi 9/9/2012, Nikkan Sports 9/9/2012, Sanspo 9/9/2012