From ESPN Chat:
Jordan:(Boston, Ma): Who are the Celtics going for in free agency?
David Aldridge: I hear they're trying to figure out a sign and trade scenario for Stromile Swift, but a half-dozen teams are doing the same thing, and Jerry West keeps telling everybody he'll match any mid-level offer sheet.
If West will match any offer, that means to get him we'll likely have to sign him for more than that and throw in players (and a pick?) to make it work. Stro is playing this smart by not signing yet. Some team like the C's will pay more for him to secure a PF.