Question: What was held at the United Center in Chicago, Illinois on June 23-24, 2017 and resulted in Sebastian Aho playing under contract as a prospect of the New York Islanders?
Sentence (from "Sebastian Aho (ice hockey, born 1996)"): Sebastian Aho (born 17 February 1996) is a Swedish professional ice hockey defenceman who is currently playing under contract as a prospect of the New York Islanders in the National Hockey League (NHL).
Relevant evidence: Yes