PITTSBURGH (AP) — Pirates pitcher Francisco Liriano has left his start in the fourth inning with discomfort on his right side.

The left-hander bent over and held his back after throwing a pitch to Chicago Cubs first baseman Anthony Rizzo on Tuesday night. Liriano stretched his back and threw a few warmup pitches while manager Clint Hurdle and athletic trainers looked on. Liriano then shook his head and left the mound.

After leading the Pirates with 16 wins last season, Liriano has struggled this year. He was 1-6 with a 4.54 ERA in 13 starts going into Tuesday’s game.

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