Just for reference, I copied Wikipedia for the Welker trade below:
On March 1, 2007, the Dolphins offered Welker, a restricted free agent, a second-round tender of $1.35 million for a one-year contract. News reports indicated the New England Patriots, who were interested in Welker, had originally considered signing him to an offer sheet (Miami would have had seven days to match the offer); according to
The Boston Globe, that sheet would have contained a
poison pill provision that would have made the offer difficult for the Dolphins to match.
[25] Ultimately, however, the Patriots decided not to use such an offer and traded their 2007 second-round draft pick and a seventh-round draft pick to the Dolphins for Welker.