Yuya Ishii left tonight’s game against the Orix Buffaloes at Sapporo Dome after developing pain in his right hamstring. Ishii entered the game in relief in the sixth inning. He began reaching for his hamstring after he got the first batter he faced, Masataka Yoshida, to ground out to second. He left the game after just five pitches.
Source: Nikkan Sports 9/13/2016
[UPDATE 9/14/2016 @ 7:21pm]
Ishii was examined at a hospital in Sapporo today and diagnosed with a strain in his right semitendinosus muscle (hamstring). He was taken off the active roster on the same day. He will require a week to two weeks for a full recovery.
Source: Daily Sports 9/14/2016