Just three games into his career, Matthew Schaefer has put the rest of the NHL on notice.

Expectations were not low for the No. 1 pick, but Schaefer’s first three games with the Islanders have eclipsed anything that anyone thought he would do right away.

The time-tested cliché is that defensemen need time to develop. It’s especially difficult for an 18-year-old to come into the league and make an impact right away. Healthy-scratching your first-round pick regularly is a popular way to integrate them into the league: No. 2 overall pick Michael Misa sat out San Jose’s first two games, and No. 5 overall Brady Martin has sat out Nashville’s past two.

That is not an option for the Islanders with Schaefer right now. It would mean scratching the player who has been their best defenseman.