Aside from the fact that the Knicks just hired Brunson's dad as an assistant coach, the Mavs playmaker and scorer has another connection to New York: Derrick Rose.
When Rose was still with the Chicago Bulls, he formed a friendship with the young Brunson, whose father Rick was working as an assistant to Tom Thibodeau–similar to the current role he now has with the Knicks.
“Jalen would go over to the Bulls facility and practice with the Bulls players,” Pat Ambrose, Brunson's coach at Adlai Stevenson High School, told the New York Post. “That’s where he became good friends with Derrick Rose. So your story gets deep with the Knicks. Derrick saw that young Jalen was a very, very good player and Derrick was a Chicago kid, and really started to mentor Jalen basketball-wise.”
The Knicks are already doing their best to create cap space in order to give Jalen Brunson a lucrative offer he can't reject. And given all the connection he has with the franchise, including the Derrick Rose tidbit, the Mavs could certainly struggle stopping him from moving to New York.
Of course a lot can happen in free agency and nothing is set in stone, though things are surely not looking so good for the Mavs right now.