The transition tag is a one-year tender offer that is the average of the top 10 salaries at the position. It guarantees the original club the right of first refusal to match any offer the player might receive from another team. The original club does not receive compensation if they do not choose to match an outside offer.
The Bills vastly overpaid for Clay's services, and the Dolphins' decision on Tuesday presents the possibility that the same thing can happen with Vernon. Of course, the Dolphins could also just end up having another team do their work for them, matching any offer for Vernon and keeping the talented pass rusher in-house.