Claire Thompson, one of three finalists for the PWHL’s defender of the year, became the first player to sign with an expansion team during the exclusive negotiating window on Wednesday.

Thompson, an anchor for the Frost as they won their second straight Walter Cup, finished third in points (18) among all PWHL blue liners, signed a one-year deal with Vancouver, which with Seattle will select at least seven players from among the league’s original six teams in Monday’s expansion draft.

“Claire is one of the best defenders in the world and a phenomenal leader who will help create a culture of excellence in Vancouver,” Vancouver general manager Sara Gardner Morey, Thompson’s coach at Princeton.

The Frost have protected Kendall Coyne Schofield, Lee Stecklein and Taylor Heise from the expansion draft and are now closer to being able to protect a fourth. Teams can protect a fourth player after losing two in free agency or the expansion draft.

Thompson, 27, had 14 assists the season, tied with Heise for second among Frost players and one behind defender Sophie Jaques.