Back when Thunder General Manager Sam Presti and I were in high school, “promise rings” were a thing guys gave to their girlfriends. Supposedly, it was an inherent agreement that the happy couple would someday get married, essentially an engagement ring for an engagement ring. In reality, it was usually an effort by the dude to convince his prudish other half to accent to him moving forward a base. I bet Sam Presti handed out a lot of those rings.
In the NBA, the draft promise is a similar concept. An NBA team zeroes in on the player they want and make an arrangement with the player’s representatives to “shut down” their draft workouts. The promise is that if the player is still available at a certain draft position that the team controls, that team will select the player. In return, the player and his agent will make no efforts to convince a team drafting earlier to choose said player.