The fireballer committed a throwing error in the eighth inning of an eventual 1-0 loss to the Pittsburgh Pirates, and was then visibly upset when instructed to intentionally walk the next batter with two outs.
Pitching coach Bob McClure took a trip to the mound in an attempt to calm down the right-hander, who wiggled out of the jam with a strikeout after issuing a walk to load the bases.
Giles was confronted by manager Ryne Sandberg and McClure upon his return to the bench, prompting a heated exchange.
"There was some frustration and some game situation," Sandberg told reporters after the loss. "We talked about some game situations. I do like to have players with emotions, but there's a time and a place and a situation to show that."
Giles was not made available for comment following the game.