[3] On January 15, 2015, Polster was selected as the 7th overall pick by the Chicago Fire during the 2015 MLS SuperDraft and was signed to a contract on February 4.

[4] On July 31, 2016, Polster scored his first career MLS goal in a 2–2 draw against the New York Red Bulls.

[11] In order to sign Polster, the Revolution had to trade $100,000 in General Allocation Money to his former club Chicago Fire for his rights.

[12] In January 2016, Polster received his first call up to the senior United States squad for friendlies against Iceland and Canada.

Two years later, he was called into January camp again for a friendly against Bosnia and Herzegovina, making his debut in the 0–0 draw.